On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
OK, even if you can't separate the pump from the valves, you may
The isolatiion valve is separate from the pump and not part of
it. The pump ends with a flange with a male thread on the
outside, like this.
https://www.screwfix.com/p/grundfos-light-commercial-central-heating-pump/1902p
Yep.
Yep, that matches what I saw.
The isolation valve has a captive ring-nut which screws onto the
pump's flange.
https://www.screwfix.com/p/flomasta-gate-pump-valve-22mm-x/81629.
Easy to say...
To separate the two you need to find a way of preventing the pump
body from rotating[1] and then use a hammer-assisted spanner on
the ring-nut.
Provided that (a) the isolation valves work and (b) that you canIf we could separate them...
separate them from the pump by the method described above, you
can change the pump without draining down.
[1] Such as by using a strap-wrench of the type used for removing
car oil filters.
That is what we have not been able to do. The threads will not
separate. But thanks for confirming the arrangement of the valve
and flange, it is exactly what we have.
still be able to change the pump without draining down.
You'll need to turn off both valves on all radiators to stop them
emptying and, assuming it's an open vented system, you'll need to
bung up the outlet from the fill & expansion tank and bung up the
open end of the inverted J shaped exansion pipe. You can then break
the system in *one* place with very little loss of water.
You need to go armed with the new pump and two new isolation
valves. Turn off both existing and both new valves. You can then
undo the compression nut on one of the old valves and, assuming
there's enough movement in the pipes, separate it from the pipe
and immediately fit one of the new valves in its place - using the
original olive and compression nut. Then do the same with the
other one, and remove the pump complete with its two valves.
Immediately fit the other new valve.
You'll then have two isolation valves at the right spacing to slide
the new pump - along with two rubber washers - into position and do
up the ring-nuts.
Then, turn the radiators on again, unbung the bunged up bits, turn
on the isolation valves - and the job's a good'un!
Don't suppose you have any photos of the existing pump installation
which you could post somewhere with a link here? That you give us a
better idea as to how much of the above is feasilble.
If the system is *really* old, you may have imperial sized pipes
rather than metric - which could present some additional
challenges!
Reply No 1, No 2 to follow later.
The last item has been worrying me. The system was built in 1976,
when the house was converted to flats, and that had me thinking
about the piping used. Does 22mm copper pipe correspond to a 1976
Imperial pipe size? I have been looking at various charts, and have
only got very confused.
I have an old photo, and I have asked for a newer one to be made
available, but that has not happened yet.
I had a Dropbox account, but it has lapsed.If the pipe is imperial it will be 3/4" nominal - which is actally
What is a good alternative place to put photos for general viewing?
larger than 3/4" in reality, and *slightly* smaller than 22mm. If
connecting one to the other with soldered joints you need special
fittings with 3/4" one end and 22mm the other end. With compression
joints there's a bit more leeway. A 22mm fitting is ok on a 3/4" pipe
(but not the other way round) but you need special olives with a
slightly smaller ID. You'd probably get away with replacing an
imperial pump valve with a metric one because the 3/4" olive already
on the pipe should be ok, and the compression nut threads will almost certainly be the same.
[Mr Google thinks that the imperial/metric change was made in 1972 -
so your system is pretty certainly metric.]
For posting photos I always use Box - which is similar to Dropbox -
but there are other free options. Hopefully someone who knows more
about it than I do will come along . . .
I had wondered if there might be an airlock, but the fill and
expansion tank is directly above the cupboard that contains the boiler,
pump and the storage tank etc, so I don't see how there could be an
airlock that does not instantly bleed out.
On 03/01/2026 10:19, Davey wrote:
<snip>
I had wondered if there might be an airlock, but the fill andThe fill and expansion tank is for the water supply for the boiler
expansion tank is directly above the cupboard that contains the
boiler, pump and the storage tank etc, so I don't see how there
could be an airlock that does not instantly bleed out.
and radiators. There should be another source of water for the tank contents that goes to the hot water taps. Have you checked that the
second source is sufficiently full? If it isn't the hot taps should
stop running, so that is probably the easiest to check.
Perhaps the zone valve isn't opening to heat the water? Try opening
it manually and leave it hooked open and see if there is hot water
after running the boiler a bit? Also, check the programmer settings.
On my system the Hot Water ON/OFF circuit controls the zone valve on
the hot water circuit and the Heating one controls the circulating
pump for heated water to the radiators, so that I can have one or
other or both in operation. I have never tried the hot radiators and
no hot water option, but that is the scenario controlled by the frost thermostat to stop the system freezing if I am away for any length of
time in the winter. Either controller being on will allow the gas
through to heat the boiler.
As an aside, I did use the microswitch circuit in the zone valve, it
lights a neon when the hot water control is ON and the tank
thermostat interrupts the zone valve circuit when there is sufficient
hot water in the tank. In a nutshell, if the neon is off then either
the hot water ON/OFF is off or there is insufficient hot water which
causes the thermostat fitted half way up the tank to demand heat.
The default of the neon being on is to show that there is over half a
tankful of hot water available and it will reheat if I use enough hot
water to have more than the bottom half of the tank refilled with
cold. It gives me an at-a-glance reassurance that the hot taps will
deliver hot water.
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.If the pipe is imperial it will be 3/4" nominal - which is actally
OK, even if you can't separate the pump from the valves, you may
The isolatiion valve is separate from the pump and not part of
it. The pump ends with a flange with a male thread on the
outside, like this.
https://www.screwfix.com/p/grundfos-light-commercial-central-heating-pump/1902p
Yep.
Yep, that matches what I saw.
The isolation valve has a captive ring-nut which screws onto the
pump's flange.
https://www.screwfix.com/p/flomasta-gate-pump-valve-22mm-x/81629.
Easy to say...
To separate the two you need to find a way of preventing the pump
body from rotating[1] and then use a hammer-assisted spanner on
the ring-nut.
Provided that (a) the isolation valves work and (b) that you canIf we could separate them...
separate them from the pump by the method described above, you
can change the pump without draining down.
[1] Such as by using a strap-wrench of the type used for removing
car oil filters.
That is what we have not been able to do. The threads will not
separate. But thanks for confirming the arrangement of the valve
and flange, it is exactly what we have.
still be able to change the pump without draining down.
You'll need to turn off both valves on all radiators to stop them
emptying and, assuming it's an open vented system, you'll need to
bung up the outlet from the fill & expansion tank and bung up the
open end of the inverted J shaped exansion pipe. You can then break
the system in *one* place with very little loss of water.
You need to go armed with the new pump and two new isolation
valves. Turn off both existing and both new valves. You can then
undo the compression nut on one of the old valves and, assuming
there's enough movement in the pipes, separate it from the pipe
and immediately fit one of the new valves in its place - using the
original olive and compression nut. Then do the same with the
other one, and remove the pump complete with its two valves.
Immediately fit the other new valve.
You'll then have two isolation valves at the right spacing to slide
the new pump - along with two rubber washers - into position and do
up the ring-nuts.
Then, turn the radiators on again, unbung the bunged up bits, turn
on the isolation valves - and the job's a good'un!
Don't suppose you have any photos of the existing pump installation
which you could post somewhere with a link here? That you give us a
better idea as to how much of the above is feasilble.
If the system is *really* old, you may have imperial sized pipes
rather than metric - which could present some additional
challenges!
Reply No 1, No 2 to follow later.
The last item has been worrying me. The system was built in 1976,
when the house was converted to flats, and that had me thinking
about the piping used. Does 22mm copper pipe correspond to a 1976
Imperial pipe size? I have been looking at various charts, and have
only got very confused.
I have an old photo, and I have asked for a newer one to be made
available, but that has not happened yet.
I had a Dropbox account, but it has lapsed.
What is a good alternative place to put photos for general viewing?
larger than 3/4" in reality, and *slightly* smaller than 22mm. If
connecting one to the other with soldered joints you need special
fittings with 3/4" one end and 22mm the other end. With compression
joints there's a bit more leeway. A 22mm fitting is ok on a 3/4" pipe
(but not the other way round) but you need special olives with a
slightly smaller ID. You'd probably get away with replacing an
imperial pump valve with a metric one because the 3/4" olive already
on the pipe should be ok, and the compression nut threads will almost
certainly be the same.
[Mr Google thinks that the imperial/metric change was made in 1972 -
so your system is pretty certainly metric.]
For posting photos I always use Box - which is similar to Dropbox -
but there are other free options. Hopefully someone who knows more
about it than I do will come along . . .
Update.
The resident in the flat managed to get a plumber yesterday, and he
succeeded in changing out the pump. The reason that we could not was
because the nuts that hold the pump and the isolating valves had been cemented or glued in place, and so the valves had to be replaced at the
same time. Now the pump runs, but the storage tank does not get hot. The resident is not electrically-trained in any way at all, so has no way
of checking what is or is not happening. He suspects the tank 'stat
wiring. I hope to find out tomorrow.
He will try today to engage an electrician for next week, I plan on
going there tomorrow if no electrician is forthcoming.
But there is progress!
Now I have a spare set of valves, and a very wide mouth adjustable
spanner purchased to better attack the pump securing nuts. But you can
never have too many tools.
I had wondered if there might be an airlock, but the fill and
expansion tank is directly above the cupboard that contains the boiler,
pump and the storage tank etc, so I don't see how there could be an
airlock that does not instantly bleed out.
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.If the pipe is imperial it will be 3/4" nominal - which is actally
OK, even if you can't separate the pump from the valves, you may
The isolatiion valve is separate from the pump and not part of
it. The pump ends with a flange with a male thread on the
outside, like this.
https://www.screwfix.com/p/grundfos-light-commercial-central-heating-pump/1902p
Yep.
Yep, that matches what I saw.
The isolation valve has a captive ring-nut which screws onto
the pump's flange.
https://www.screwfix.com/p/flomasta-gate-pump-valve-22mm-x/81629. >>>>>>
Easy to say...
To separate the two you need to find a way of preventing the
pump body from rotating[1] and then use a hammer-assisted
spanner on the ring-nut.
Provided that (a) the isolation valves work and (b) that youIf we could separate them...
can separate them from the pump by the method described above,
you can change the pump without draining down.
[1] Such as by using a strap-wrench of the type used for
removing car oil filters.
That is what we have not been able to do. The threads will not
separate. But thanks for confirming the arrangement of the valve
and flange, it is exactly what we have.
still be able to change the pump without draining down.
You'll need to turn off both valves on all radiators to stop them
emptying and, assuming it's an open vented system, you'll need to
bung up the outlet from the fill & expansion tank and bung up the
open end of the inverted J shaped exansion pipe. You can then
break the system in *one* place with very little loss of water.
You need to go armed with the new pump and two new isolation
valves. Turn off both existing and both new valves. You can then
undo the compression nut on one of the old valves and, assuming
there's enough movement in the pipes, separate it from the pipe
and immediately fit one of the new valves in its place - using
the original olive and compression nut. Then do the same with the
other one, and remove the pump complete with its two valves.
Immediately fit the other new valve.
You'll then have two isolation valves at the right spacing to
slide the new pump - along with two rubber washers - into
position and do up the ring-nuts.
Then, turn the radiators on again, unbung the bunged up bits,
turn on the isolation valves - and the job's a good'un!
Don't suppose you have any photos of the existing pump
installation which you could post somewhere with a link here?
That you give us a better idea as to how much of the above is
feasilble.
If the system is *really* old, you may have imperial sized pipes
rather than metric - which could present some additional
challenges!
Reply No 1, No 2 to follow later.
The last item has been worrying me. The system was built in 1976,
when the house was converted to flats, and that had me thinking
about the piping used. Does 22mm copper pipe correspond to a 1976
Imperial pipe size? I have been looking at various charts, and
have only got very confused.
I have an old photo, and I have asked for a newer one to be made
available, but that has not happened yet.
I had a Dropbox account, but it has lapsed.
What is a good alternative place to put photos for general
viewing?
larger than 3/4" in reality, and *slightly* smaller than 22mm. If
connecting one to the other with soldered joints you need special
fittings with 3/4" one end and 22mm the other end. With compression
joints there's a bit more leeway. A 22mm fitting is ok on a 3/4"
pipe (but not the other way round) but you need special olives
with a slightly smaller ID. You'd probably get away with replacing
an imperial pump valve with a metric one because the 3/4" olive
already on the pipe should be ok, and the compression nut threads
will almost certainly be the same.
[Mr Google thinks that the imperial/metric change was made in 1972
- so your system is pretty certainly metric.]
For posting photos I always use Box - which is similar to Dropbox -
but there are other free options. Hopefully someone who knows more
about it than I do will come along . . .
Update.
The resident in the flat managed to get a plumber yesterday, and he succeeded in changing out the pump. The reason that we could not was because the nuts that hold the pump and the isolating valves had
been cemented or glued in place, and so the valves had to be
replaced at the same time. Now the pump runs, but the storage tank
does not get hot. The resident is not electrically-trained in any
way at all, so has no way of checking what is or is not happening.
He suspects the tank 'stat wiring. I hope to find out tomorrow.
He will try today to engage an electrician for next week, I plan on
going there tomorrow if no electrician is forthcoming.
But there is progress!
Now I have a spare set of valves, and a very wide mouth adjustable
spanner purchased to better attack the pump securing nuts. But you
can never have too many tools.
I had wondered if there might be an airlock, but the fill and
expansion tank is directly above the cupboard that contains the
boiler, pump and the storage tank etc, so I don't see how there
could be an airlock that does not instantly bleed out.
Looking back at all the posts in this thread, I don't think that
you've ever said what type of control system is in place - how many
zones valves there are and whether it/they are the 2-port or 3-port
type.
Going by the age of the system and by your assertion that the valve
doesn't use microswitches, my hunch is that you have a W-Plan system
which has a single 3-port diverter valve. See https://wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning#DHW_priority:_W-Plan
This can heat either the hot water or the radiators but not both at
the same time. The valve is controlled by the cylinder thermostat. If
the stat is not satisfied, the valve is in the unenergised HW
position so the cylinder gets heated. Once the stat is satisfied, it energises the valve which then moves to the CH position and heats the radiators.
In the event of an air lock in the HW circuit which prevented the
cylinder from getting hot (unlikely) the stat would never be
satisfied, so the radiators wouldn't be heated either.
Assuming my hunch about it being a W-Plan system is correct, if the radiators get hot but the cylinder doesn't, either the wet part of
the valve is stuck in the CH position, or the cylinder stat is
telling the valve that the HW is hot when it isn't. This could be a
wiring problem - but unlikely if it worked in the past and the wiring
has not been disturbed, or maybe the stat's contacts could have
welded themselves closed so that it is always "satisfied" even when
the water is cold.
If you don't think it's a W-Plan system, please tell us what it
actually is.
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.If the pipe is imperial it will be 3/4" nominal - which is actally
OK, even if you can't separate the pump from the valves, you may
The isolatiion valve is separate from the pump and not part of >>>>>>>> it. The pump ends with a flange with a male thread on the
outside, like this.
https://www.screwfix.com/p/grundfos-light-commercial-central-heating-pump/1902p
Yep.
Yep, that matches what I saw.
The isolation valve has a captive ring-nut which screws onto
the pump's flange.
https://www.screwfix.com/p/flomasta-gate-pump-valve-22mm-x/81629. >>>>>>>>
Easy to say...
To separate the two you need to find a way of preventing the
pump body from rotating[1] and then use a hammer-assisted
spanner on the ring-nut.
Provided that (a) the isolation valves work and (b) that youIf we could separate them...
can separate them from the pump by the method described above, >>>>>>>> you can change the pump without draining down.
[1] Such as by using a strap-wrench of the type used for
removing car oil filters.
That is what we have not been able to do. The threads will not
separate. But thanks for confirming the arrangement of the valve >>>>>>> and flange, it is exactly what we have.
still be able to change the pump without draining down.
You'll need to turn off both valves on all radiators to stop them
emptying and, assuming it's an open vented system, you'll need to
bung up the outlet from the fill & expansion tank and bung up the
open end of the inverted J shaped exansion pipe. You can then
break the system in *one* place with very little loss of water.
You need to go armed with the new pump and two new isolation
valves. Turn off both existing and both new valves. You can then
undo the compression nut on one of the old valves and, assuming
there's enough movement in the pipes, separate it from the pipe
and immediately fit one of the new valves in its place - using
the original olive and compression nut. Then do the same with the
other one, and remove the pump complete with its two valves.
Immediately fit the other new valve.
You'll then have two isolation valves at the right spacing to
slide the new pump - along with two rubber washers - into
position and do up the ring-nuts.
Then, turn the radiators on again, unbung the bunged up bits,
turn on the isolation valves - and the job's a good'un!
Don't suppose you have any photos of the existing pump
installation which you could post somewhere with a link here?
That you give us a better idea as to how much of the above is
feasilble.
If the system is *really* old, you may have imperial sized pipes
rather than metric - which could present some additional
challenges!
Reply No 1, No 2 to follow later.
The last item has been worrying me. The system was built in 1976,
when the house was converted to flats, and that had me thinking
about the piping used. Does 22mm copper pipe correspond to a 1976
Imperial pipe size? I have been looking at various charts, and
have only got very confused.
I have an old photo, and I have asked for a newer one to be made
available, but that has not happened yet.
I had a Dropbox account, but it has lapsed.
What is a good alternative place to put photos for general
viewing?
larger than 3/4" in reality, and *slightly* smaller than 22mm. If
connecting one to the other with soldered joints you need special
fittings with 3/4" one end and 22mm the other end. With compression
joints there's a bit more leeway. A 22mm fitting is ok on a 3/4"
pipe (but not the other way round) but you need special olives
with a slightly smaller ID. You'd probably get away with replacing
an imperial pump valve with a metric one because the 3/4" olive
already on the pipe should be ok, and the compression nut threads
will almost certainly be the same.
[Mr Google thinks that the imperial/metric change was made in 1972
- so your system is pretty certainly metric.]
For posting photos I always use Box - which is similar to Dropbox -
but there are other free options. Hopefully someone who knows more
about it than I do will come along . . .
Update.
The resident in the flat managed to get a plumber yesterday, and he
succeeded in changing out the pump. The reason that we could not was
because the nuts that hold the pump and the isolating valves had
been cemented or glued in place, and so the valves had to be
replaced at the same time. Now the pump runs, but the storage tank
does not get hot. The resident is not electrically-trained in any
way at all, so has no way of checking what is or is not happening.
He suspects the tank 'stat wiring. I hope to find out tomorrow.
He will try today to engage an electrician for next week, I plan on
going there tomorrow if no electrician is forthcoming.
But there is progress!
Now I have a spare set of valves, and a very wide mouth adjustable
spanner purchased to better attack the pump securing nuts. But you
can never have too many tools.
I had wondered if there might be an airlock, but the fill and
expansion tank is directly above the cupboard that contains the
boiler, pump and the storage tank etc, so I don't see how there
could be an airlock that does not instantly bleed out.
Looking back at all the posts in this thread, I don't think that
you've ever said what type of control system is in place - how many
zones valves there are and whether it/they are the 2-port or 3-port
type.
Going by the age of the system and by your assertion that the valve
doesn't use microswitches, my hunch is that you have a W-Plan system
which has a single 3-port diverter valve. See
https://wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning#DHW_priority:_W-Plan
This can heat either the hot water or the radiators but not both at
the same time. The valve is controlled by the cylinder thermostat. If
the stat is not satisfied, the valve is in the unenergised HW
position so the cylinder gets heated. Once the stat is satisfied, it
energises the valve which then moves to the CH position and heats the
radiators.
In the event of an air lock in the HW circuit which prevented the
cylinder from getting hot (unlikely) the stat would never be
satisfied, so the radiators wouldn't be heated either.
Assuming my hunch about it being a W-Plan system is correct, if the
radiators get hot but the cylinder doesn't, either the wet part of
the valve is stuck in the CH position, or the cylinder stat is
telling the valve that the HW is hot when it isn't. This could be a
wiring problem - but unlikely if it worked in the past and the wiring
has not been disturbed, or maybe the stat's contacts could have
welded themselves closed so that it is always "satisfied" even when
the water is cold.
If you don't think it's a W-Plan system, please tell us what it
actually is.
I did not find an exact version of the system. It is like a 'C'Plan,
without the microswitch being used. A 'W' Plan uses a diverter valve,
here there is only one 2-port valve, which lets hot water from the
boiler circuit out to the radiators. The Tank 'stat controls the pump
and boiler, DHW has to be On for heat in the system, and the timer does
that. If the timer also asks for CH, then the Room 'stat opens the
one valve, which then lets hot water out to the radiator loop.
I am first going to check the valves etc for simple mistakes, such
as closed valves, then operate the system and see what does and does
not happen, hoping to do a system debug.
Note that I said that the timer had been replaced, the 'new' one
having a much more crowded terminal strip, so all the wiring is
untested.
With luck, I will be able to get it working.
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.If the pipe is imperial it will be 3/4" nominal - which is
OK, even if you can't separate the pump from the valves, you
The isolatiion valve is separate from the pump and not part
of it. The pump ends with a flange with a male thread on the >>>>>>>> outside, like this.
https://www.screwfix.com/p/grundfos-light-commercial-central-heating-pump/1902p
Yep.
Yep, that matches what I saw.
The isolation valve has a captive ring-nut which screws onto >>>>>>>> the pump's flange.
https://www.screwfix.com/p/flomasta-gate-pump-valve-22mm-x/81629. >>>>>>>>
Easy to say...
To separate the two you need to find a way of preventing the >>>>>>>> pump body from rotating[1] and then use a hammer-assisted
spanner on the ring-nut.
Provided that (a) the isolation valves work and (b) that you >>>>>>>> can separate them from the pump by the method describedIf we could separate them...
above, you can change the pump without draining down.
[1] Such as by using a strap-wrench of the type used for
removing car oil filters.
That is what we have not been able to do. The threads will not >>>>>>> separate. But thanks for confirming the arrangement of the
valve and flange, it is exactly what we have.
may still be able to change the pump without draining down.
You'll need to turn off both valves on all radiators to stop
them emptying and, assuming it's an open vented system, you'll
need to bung up the outlet from the fill & expansion tank and
bung up the open end of the inverted J shaped exansion pipe.
You can then break the system in *one* place with very little
loss of water.
You need to go armed with the new pump and two new isolation
valves. Turn off both existing and both new valves. You can
then undo the compression nut on one of the old valves and,
assuming there's enough movement in the pipes, separate it
from the pipe and immediately fit one of the new valves in its
place - using the original olive and compression nut. Then do
the same with the other one, and remove the pump complete with
its two valves. Immediately fit the other new valve.
You'll then have two isolation valves at the right spacing to
slide the new pump - along with two rubber washers - into
position and do up the ring-nuts.
Then, turn the radiators on again, unbung the bunged up bits,
turn on the isolation valves - and the job's a good'un!
Don't suppose you have any photos of the existing pump
installation which you could post somewhere with a link here?
That you give us a better idea as to how much of the above is
feasilble.
If the system is *really* old, you may have imperial sized
pipes rather than metric - which could present some additional
challenges!
Reply No 1, No 2 to follow later.
The last item has been worrying me. The system was built in
1976, when the house was converted to flats, and that had me
thinking about the piping used. Does 22mm copper pipe
correspond to a 1976 Imperial pipe size? I have been looking at
various charts, and have only got very confused.
I have an old photo, and I have asked for a newer one to be made
available, but that has not happened yet.
I had a Dropbox account, but it has lapsed.
What is a good alternative place to put photos for general
viewing?
actally larger than 3/4" in reality, and *slightly* smaller than
22mm. If connecting one to the other with soldered joints you
need special fittings with 3/4" one end and 22mm the other end.
With compression joints there's a bit more leeway. A 22mm
fitting is ok on a 3/4" pipe (but not the other way round) but
you need special olives with a slightly smaller ID. You'd
probably get away with replacing an imperial pump valve with a
metric one because the 3/4" olive already on the pipe should be
ok, and the compression nut threads will almost certainly be the
same.
[Mr Google thinks that the imperial/metric change was made in
1972
- so your system is pretty certainly metric.]
For posting photos I always use Box - which is similar to
Dropbox - but there are other free options. Hopefully someone
who knows more about it than I do will come along . . .
Update.
The resident in the flat managed to get a plumber yesterday, and
he succeeded in changing out the pump. The reason that we could
not was because the nuts that hold the pump and the isolating
valves had been cemented or glued in place, and so the valves had
to be replaced at the same time. Now the pump runs, but the
storage tank does not get hot. The resident is not
electrically-trained in any way at all, so has no way of checking
what is or is not happening. He suspects the tank 'stat wiring. I
hope to find out tomorrow. He will try today to engage an
electrician for next week, I plan on going there tomorrow if no
electrician is forthcoming. But there is progress!
Now I have a spare set of valves, and a very wide mouth adjustable
spanner purchased to better attack the pump securing nuts. But you
can never have too many tools.
I had wondered if there might be an airlock, but the fill and
expansion tank is directly above the cupboard that contains the
boiler, pump and the storage tank etc, so I don't see how there
could be an airlock that does not instantly bleed out.
Looking back at all the posts in this thread, I don't think that
you've ever said what type of control system is in place - how many
zones valves there are and whether it/they are the 2-port or 3-port
type.
Going by the age of the system and by your assertion that the valve
doesn't use microswitches, my hunch is that you have a W-Plan
system which has a single 3-port diverter valve. See
https://wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning#DHW_priority:_W-Plan
This can heat either the hot water or the radiators but not both at
the same time. The valve is controlled by the cylinder thermostat.
If the stat is not satisfied, the valve is in the unenergised HW
position so the cylinder gets heated. Once the stat is satisfied,
it energises the valve which then moves to the CH position and
heats the radiators.
In the event of an air lock in the HW circuit which prevented the
cylinder from getting hot (unlikely) the stat would never be
satisfied, so the radiators wouldn't be heated either.
Assuming my hunch about it being a W-Plan system is correct, if the
radiators get hot but the cylinder doesn't, either the wet part of
the valve is stuck in the CH position, or the cylinder stat is
telling the valve that the HW is hot when it isn't. This could be a
wiring problem - but unlikely if it worked in the past and the
wiring has not been disturbed, or maybe the stat's contacts could
have welded themselves closed so that it is always "satisfied"
even when the water is cold.
If you don't think it's a W-Plan system, please tell us what it
actually is.
I did not find an exact version of the system. It is like a 'C'Plan, without the microswitch being used. A 'W' Plan uses a diverterMm - I'm totally mystified as to what you *have* got.
valve, here there is only one 2-port valve, which lets hot water
from the boiler circuit out to the radiators. The Tank 'stat
controls the pump and boiler, DHW has to be On for heat in the
system, and the timer does that. If the timer also asks for CH,
then the Room 'stat opens the one valve, which then lets hot water
out to the radiator loop. I am first going to check the valves etc
for simple mistakes, such as closed valves, then operate the system
and see what does and does not happen, hoping to do a system debug.
Note that I said that the timer had been replaced, the 'new' one
having a much more crowded terminal strip, so all the wiring is
untested.
With luck, I will be able to get it working.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even if
the room stat has opened the zone valve. That surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire go
which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the stat
is satisfied, what stops the hot water from getting too hot (assuming
that the boiler flow temperature to the rads is higher than the
desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even if
the room stat has opened the zone valve. That surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire go
which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the stat
is satisfied, what stops the hot water from getting too hot (assuming
that the boiler flow temperature to the rads is higher than the
desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even if
the room stat has opened the zone valve. That surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire go
which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the stat
is satisfied, what stops the hot water from getting too hot (assuming
that the boiler flow temperature to the rads is higher than the
desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them somehow (I wasn't there) and then removed the resin'ed remains from the valves,
along with the dead pump. Then he took the two new valves, and knew how
to separate the nuts from the valves. Neat trick. These then went on the
old valves, the new pump was installed as normal.
2. When the pump was connected, and the timer set to All on, the pump
ran, and unlike the old one, has a display, showing what appears to be
a discharge pressure. This was varying from 5 to 13 or so. I had
checked the isolation valves, and the tank feed valve, and they were
all open. The boiler would light, and then go out.
3. To cut a long story short, the whole system was one big airlock.
Bleeding air from the three radiators in rotation resulted in the boiler finally staying on, and then with the zone valve opened by the room
'stat, heat began to be felt in the radiators. The pump was
displaying a steady reading of 6.0 somethings. Being happy that the
system was at least operating, I left for home. Soon after I arrived
here, 90 minutes later, Simon called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is exactly how
the system was, and is again, wired. It worked for Simon all through
last winter, and he had no reason to query it. In a perfect world, a
better way would be found, but "if it ain't broke, don't fix it".
5. I don't see your problem with the current Tank 'stat/pump/boiler arrangement. If the tank gets to setpoint, it will shut the pump and
boiler down, so I don't see runaway happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre', aka J-Box, to improve and neaten the wiring to the replacement timer, as its
very small terminals do not enable good tidy connections directly to it, whereas the old one had large terminals. But the new J-box has
equally small terminals, offering little if any improvement. Back to
the drawing board. I need to source a J-Box with larger internal
connectors.
7. The Boiler/pump/valve radiator layout is as I have described it*. It
does not conform to any of the published layouts. It is closest to a 'C'-Plan, but with a different valve arrangement. That is why I cannot
name the Plan.
* The pump takes hot water from the boiler and sends it through the
tank heater coil, and back to the boiler. Just before the entry to
the boiler, there is a 'T' and the zone valve takes off from that
point to go to the radiators. That's it. I didn't design it.
I need a drink.
On 04/01/2026 17:43, Davey wrote:I agree that the room 'stat/valve/boiler control is not theoretically
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even
if the room stat has opened the zone valve. That surely can't be
right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire
go which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the
stat is satisfied, what stops the hot water from getting too hot
(assuming that the boiler flow temperature to the rads is higher
than the desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them
somehow (I wasn't there) and then removed the resin'ed remains from
the valves, along with the dead pump. Then he took the two new
valves, and knew how to separate the nuts from the valves. Neat
trick. These then went on the old valves, the new pump was
installed as normal. 2. When the pump was connected, and the timer
set to All on, the pump ran, and unlike the old one, has a display,
showing what appears to be a discharge pressure. This was varying
from 5 to 13 or so. I had checked the isolation valves, and the
tank feed valve, and they were all open. The boiler would light,
and then go out. 3. To cut a long story short, the whole system was
one big airlock. Bleeding air from the three radiators in rotation
resulted in the boiler finally staying on, and then with the zone
valve opened by the room 'stat, heat began to be felt in the
radiators. The pump was displaying a steady reading of 6.0
somethings. Being happy that the system was at least operating, I
left for home. Soon after I arrived here, 90 minutes later, Simon
called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is exactly
how the system was, and is again, wired. It worked for Simon all
through last winter, and he had no reason to query it. In a perfect
world, a better way would be found, but "if it ain't broke, don't
fix it". 5. I don't see your problem with the current Tank 'stat/pump/boiler arrangement. If the tank gets to setpoint, it
will shut the pump and boiler down, so I don't see runaway
happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre',
aka J-Box, to improve and neaten the wiring to the replacement
timer, as its very small terminals do not enable good tidy
connections directly to it, whereas the old one had large
terminals. But the new J-box has equally small terminals, offering
little if any improvement. Back to the drawing board. I need to
source a J-Box with larger internal connectors.
7. The Boiler/pump/valve radiator layout is as I have described
it*. It does not conform to any of the published layouts. It is
closest to a 'C'-Plan, but with a different valve arrangement. That
is why I cannot name the Plan.
* The pump takes hot water from the boiler and sends it through the
tank heater coil, and back to the boiler. Just before the entry
to the boiler, there is a 'T' and the zone valve takes off from that
point to go to the radiators. That's it. I didn't design it.
I need a drink.
Excellent news! So glad you got it working.
My problem with the control system is this: In order for the HW to
get hot, the boiler and pump must be running. In order to have hot radiators, the boiler and pump must be running *and* the zone valve
must be open. If the tank stat controls *only* the boiler and pump,
and the room stat controls *only* the zone valve, what tells the
boiler and pump to run for the CH once the tank stat has turned them
off? Also, since the boiler and pump need to be on to get CH (but we
don't know how!) in the absense of a zone valve in the HW circuit,
the boiler flow will continue to flow through the tank coil even
though the tank stat is satisfied. So what then stops the HW from
getting up to boiler flow temperature rather than just to the lower temperature set by the tank stat? My guess is that there's something
a bit cleverer going on than what you have described. Maybe it
doesn't matter now that it is working again - but it would be nice to understand it completely for future reference.
On Sun, 4 Jan 2026 20:26:53 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 04/01/2026 17:43, Davey wrote:
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even
if the room stat has opened the zone valve. That surely can't be
right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire
go which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the
stat is satisfied, what stops the hot water from getting too hot
(assuming that the boiler flow temperature to the rads is higher
than the desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them
somehow (I wasn't there) and then removed the resin'ed remains from
the valves, along with the dead pump. Then he took the two new
valves, and knew how to separate the nuts from the valves. Neat
trick. These then went on the old valves, the new pump was
installed as normal. 2. When the pump was connected, and the timer
set to All on, the pump ran, and unlike the old one, has a display,
showing what appears to be a discharge pressure. This was varying
from 5 to 13 or so. I had checked the isolation valves, and the
tank feed valve, and they were all open. The boiler would light,
and then go out. 3. To cut a long story short, the whole system was
one big airlock. Bleeding air from the three radiators in rotation
resulted in the boiler finally staying on, and then with the zone
valve opened by the room 'stat, heat began to be felt in the
radiators. The pump was displaying a steady reading of 6.0
somethings. Being happy that the system was at least operating, I
left for home. Soon after I arrived here, 90 minutes later, Simon
called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is exactly
how the system was, and is again, wired. It worked for Simon all
through last winter, and he had no reason to query it. In a perfect
world, a better way would be found, but "if it ain't broke, don't
fix it". 5. I don't see your problem with the current Tank
'stat/pump/boiler arrangement. If the tank gets to setpoint, it
will shut the pump and boiler down, so I don't see runaway
happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre',
aka J-Box, to improve and neaten the wiring to the replacement
timer, as its very small terminals do not enable good tidy
connections directly to it, whereas the old one had large
terminals. But the new J-box has equally small terminals, offering
little if any improvement. Back to the drawing board. I need to
source a J-Box with larger internal connectors.
7. The Boiler/pump/valve radiator layout is as I have described
it*. It does not conform to any of the published layouts. It is
closest to a 'C'-Plan, but with a different valve arrangement. That
is why I cannot name the Plan.
* The pump takes hot water from the boiler and sends it through the
tank heater coil, and back to the boiler. Just before the entry
to the boiler, there is a 'T' and the zone valve takes off from that
point to go to the radiators. That's it. I didn't design it.
I need a drink.
Excellent news! So glad you got it working.
My problem with the control system is this: In order for the HW to
get hot, the boiler and pump must be running. In order to have hot
radiators, the boiler and pump must be running *and* the zone valve
must be open. If the tank stat controls *only* the boiler and pump,
and the room stat controls *only* the zone valve, what tells the
boiler and pump to run for the CH once the tank stat has turned them
off? Also, since the boiler and pump need to be on to get CH (but we
don't know how!) in the absense of a zone valve in the HW circuit,
the boiler flow will continue to flow through the tank coil even
though the tank stat is satisfied. So what then stops the HW from
getting up to boiler flow temperature rather than just to the lower
temperature set by the tank stat? My guess is that there's something
a bit cleverer going on than what you have described. Maybe it
doesn't matter now that it is working again - but it would be nice to
understand it completely for future reference.
I agree that the room 'stat/valve/boiler control is not theoretically optimal, which is why I was thinking about it last night. But it works.
As for the runaway possibility, if the room 'stat is asking for CH
heat, then there is a load on the boiler, so it is unlikely that the
tank will run away as long as the room 'stat is asking for heat. When
the room 'stat is satisfied, the tank 'stat will have solo control of
the pump and boiler, which it already does anyway. The room 'stat does
not operate them. If the tank 'stat is satisfied, the pump and boiler
are turned off.
I am certain that the system is as I describe it, after all, I wired it
up according to my notes of it as it used to be, and I have no physical reason to doubt them.
From what I see, any idea of using the valve microswitch, however conceptually desirable, would only add complications and could lead to
the runaway condition you envisage. It was not connected to anything originally.
One thought. We don't know how long passes between the room 'stat
asking for heat and the tank 'stat asking for heat. It may be that,
once the valve is opened, it takes a while for the hot water to mingle
with the cold water in the radiator loop, and then the tank 'stat
operates. Maybe.
It may be that,I can only offer:
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe.
"It may be that,But it works. That is all I can say on the matter. How long it takes to
once the valve is opened, it takes a while for the hot water to mingle
with the cold water in the radiator loop, and then the tank 'stat
operates. Maybe."
On Sun, 4 Jan 2026 22:31:23 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe.
I can only offer:
"It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe."
But it works. That is all I can say on the matter. How long it takes
to happen, we don't know. And I'm not going to spend -u30 on petrol
going there again if I don't need to just to find out. If I go again
for some other reason, I might find time to experiment. If you want
to fund my -u30, I would consider going down again to investigate this.
On Sun, 4 Jan 2026 22:31:23 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe.
I can only offer:
"It may be that,
once the valve is opened, it takes a while for the hot water to mingle
with the cold water in the radiator loop, and then the tank 'stat
operates. Maybe."
But it works. That is all I can say on the matter. How long it takes to happen, we don't know. And I'm not going to spend -u30 on petrol going
there again if I don't need to just to find out. If I go again for some
other reason, I might find time to experiment. If you want to fund my
-u30, I would consider going down again to investigate this.
On Sun, 4 Jan 2026 23:57:01 +0000
Davey <davey@example.invalid> wrote:
On Sun, 4 Jan 2026 22:31:23 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe.
I can only offer:
"It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe."
But it works. That is all I can say on the matter. How long it takes
to happen, we don't know. And I'm not going to spend -u30 on petrol
going there again if I don't need to just to find out. If I go again
for some other reason, I might find time to experiment. If you want
to fund my -u30, I would consider going down again to investigate this.
I searched this morning for a suitable 'Wiring Centre', and I found
this: https://cpc.farnell.com/wago/mbox-l32-wiring-centre/junction-box-wiring-center-221/dp/CN22658
which looks as though it might do the job.
I would of course wire it for my non-standard system, but it appears to provide the necessary number of connectors. But I will work through it
check.
On 04/01/2026 23:57, Davey wrote:
On Sun, 4 Jan 2026 22:31:23 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe.
I can only offer:
"It may be that,
once the valve is opened, it takes a while for the hot water to
mingle with the cold water in the radiator loop, and then the tank
'stat operates. Maybe."
But it works. That is all I can say on the matter. How long it
takes to happen, we don't know. And I'm not going to spend -u30 on
petrol going there again if I don't need to just to find out. If I
go again for some other reason, I might find time to experiment. If
you want to fund my -u30, I would consider going down again to
investigate this.
I fear that I may have annoyed you with my line of
questioning/commenting. If so, it was entirely unintentional and I
apologise sincerely. Put it down to my nerd-like desire to get to the
bottom of things.
As it's now working, there's no point in making another special trip,I can assure you that the tank 'stat has only 2 wires, Live and Load.
but it would be worth having a really good look at it next time you
go -specially if you are installing a new wiring centre.
My guess is that it's designed to provide HW priority - similar to a
W-Plan system - and that the radiators don't get hot until the tank
stat is satisfied. If that is the case, the tank stat is probably a changeover switch with 3 connections rather than just on/off, and one
of the connections probably goes to the zone valve - either directly
or via the wiring centre. Hopefully you'll be able to figure it out
when you're there.
On 05/01/2026 10:11, Davey wrote:
I searched this morning for a suitable 'Wiring Centre', and I foundIt claims to be ok for S-Plan and Y-Plan systems, so it should be ok.
this:
https://cpc.farnell.com/wago/mbox-l32-wiring-centre/junction-box-
wiring-center-221/dp/CN22658
which looks as though it might do the job.
I would of course wire it for my non-standard system, but it appears to
provide the necessary number of connectors. But I will work through it
check.
However, it doesn't seem to say exactly how many connectors there are.
From memory, a conventional wiring centre with choc-block type
connectors has 10 of them, each allowing 2 or more wires to be joined together. That's not always enough, depending on the complexity of the system. For example, mine couldn't cope with 3 heating zones and I had
to install a second box.
To work out how many connectors you need, and how many wires each one
has to accommodate, you really need an accurate wiring diagram and I'm
not sure that you have one.
Roger Mills wrote:
On 05/01/2026 10:11, Davey wrote:
I searched this morning for a suitable 'Wiring Centre', and I foundIt claims to be ok for S-Plan and Y-Plan systems, so it should be
this:
https://cpc.farnell.com/wago/mbox-l32-wiring-centre/junction-box-
wiring-center-221/dp/CN22658
which looks as though it might do the job.
I would of course wire it for my non-standard system, but it
appears to provide the necessary number of connectors. But I will
work through it check.
ok.
However, it doesn't seem to say exactly how many connectors there
are. From memory, a conventional wiring centre with choc-block type connectors has 10 of them, each allowing 2 or more wires to be
joined together. That's not always enough, depending on the
complexity of the system. For example, mine couldn't cope with 3
heating zones and I had to install a second box.
To work out how many connectors you need, and how many wires each
one has to accommodate, you really need an accurate wiring diagram
and I'm not sure that you have one.
In the farnell "documents" section they show how you'd use the wagos
in a "Y" configuration, but it doesn't show an "S" version ...
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even if
the room stat has opened the zone valve. That surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire go
which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the stat
is satisfied, what stops the hot water from getting too hot (assuming
that the boiler flow temperature to the rads is higher than the
desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them somehow (I wasn't there) and then removed the resin'ed remains from the valves,
along with the dead pump. Then he took the two new valves, and knew how
to separate the nuts from the valves. Neat trick. These then went on the
old valves, the new pump was installed as normal.
2. When the pump was connected, and the timer set to All on, the pump
ran, and unlike the old one, has a display, showing what appears to be
a discharge pressure. This was varying from 5 to 13 or so. I had
checked the isolation valves, and the tank feed valve, and they were
all open. The boiler would light, and then go out.
3. To cut a long story short, the whole system was one big airlock.
Bleeding air from the three radiators in rotation resulted in the boiler finally staying on, and then with the zone valve opened by the room
'stat, heat began to be felt in the radiators. The pump was
displaying a steady reading of 6.0 somethings. Being happy that the
system was at least operating, I left for home. Soon after I arrived
here, 90 minutes later, Simon called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is exactly how
the system was, and is again, wired. It worked for Simon all through
last winter, and he had no reason to query it. In a perfect world, a
better way would be found, but "if it ain't broke, don't fix it".
5. I don't see your problem with the current Tank 'stat/pump/boiler arrangement. If the tank gets to setpoint, it will shut the pump and
boiler down, so I don't see runaway happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre', aka J-Box, to improve and neaten the wiring to the replacement timer, as its
very small terminals do not enable good tidy connections directly to it, whereas the old one had large terminals. But the new J-box has
equally small terminals, offering little if any improvement. Back to
the drawing board. I need to source a J-Box with larger internal
connectors.
7. The Boiler/pump/valve radiator layout is as I have described it*. It
does not conform to any of the published layouts. It is closest to a 'C'-Plan, but with a different valve arrangement. That is why I cannot
name the Plan.
* The pump takes hot water from the boiler and sends it through the
tank heater coil, and back to the boiler. Just before the entry to
the boiler, there is a 'T' and the zone valve takes off from that
point to go to the radiators. That's it. I didn't design it.
I need a drink.
On 04/01/2026 17:43, Davey wrote:
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
-a-a-a ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that, if
the tank stat controls the boiler and pump, once that is satisfied
the boiler and pump will stop so the radiators won't get hot even if
the room stat has opened the zone valve. That surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So it
ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire go
which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the stat
is satisfied, what stops the hot water from getting too hot (assuming
that the boiler flow temperature to the rads is higher than the
desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it is
supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them somehow (I
wasn't there) and then removed the resin'ed remains from the valves,
along with the dead pump. Then he took the two new valves, and knew how
to separate the nuts from the valves. Neat trick. These then went on the
old valves, the new pump was installed as normal.
2. When the pump was connected, and the timer set to All on, the pump
ran, and unlike the old one, has a display, showing what appears to be
a discharge pressure. This was varying from 5 to 13 or so. I had
checked the isolation valves, and the tank feed valve, and they were
all open. The boiler would light, and then go out.
3. To cut a long story short, the whole system was one big airlock.
Bleeding air from the three radiators in rotation resulted in the boiler
finally staying on, and then with the zone valve opened by the room
'stat, heat began to be felt in the radiators. The pump was
displaying a steady reading of 6.0 somethings. Being happy that the
system was at least operating, I left for home. Soon after I arrived
here, 90 minutes later, Simon called saying he now had hot water. He was
ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is exactly how
the system was, and is again, wired. It worked for Simon all through
last winter, and he had no reason to query it. In a perfect world, a
better way would be found, but "if it ain't broke, don't fix it".
5. I don't see your problem with the current Tank 'stat/pump/boiler
arrangement. If the tank gets to setpoint, it will shut the pump and
boiler down, so I don't see runaway happening. It has never knowingly
happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre', aka
J-Box, to improve and neaten the wiring to the replacement timer, as its
very small terminals do not enable good tidy connections directly to it,
whereas the old one had large terminals. But the new J-box has
equally small terminals, offering little if any improvement. Back to
the drawing board. I need to source a J-Box with larger internal
connectors.
7. The Boiler/pump/valve radiator layout is as I have described it*. It
does not conform to any of the published layouts. It is closest to a
'C'-Plan, but with a different valve arrangement. That is why I cannot
name the Plan.
* The pump takes hot water from the boiler and sends it through the
-a-a tank heater coil, and back to the boiler. Just before the entry to
-a-a the boiler, there is a 'T' and the zone valve takes off from that
-a-a point to go to the radiators. That's it. I didn't design it.
I need a drink.
With the zone valve where you said it was, I am wondering whether the
water flow through the pump is in the direction you assume it is.-a If
you imagine the flow through the pump is in the opposite direction you
have (as near as dammit) a C-plan system.
I am certain that the flow is as I described. I had to re-orientate theWith the zone valve where you said it was, I am wondering whether
the water flow through the pump is in the direction you assume it
is.-a If you imagine the flow through the pump is in the opposite
direction you have (as near as dammit) a C-plan system.
I wondered about that but dismissed it because Davey's system appears
to be fully pumped - whereas C-Plan has gravity DHW - and C-Plan has
the zone valve in the HW - not CH - circuit *and* uses the valve's microswitch.
On 06/01/2026 12:44, Indy Jess John wrote:I think I have solved the mystery. The timer does not offer
On 04/01/2026 17:43, Davey wrote:
On Sat, 3 Jan 2026 23:04:27 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 21:22, Davey wrote:
On Sat, 3 Jan 2026 18:53:48 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 03/01/2026 10:19, Davey wrote:
On Tue, 30 Dec 2025 23:45:20 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
On 30/12/2025 15:51, Davey wrote:
Snipped for brevity.
-a-a-a ed as to what you *have* got.
Are you sure that your description is correct? Seems to me that,
if the tank stat controls the boiler and pump, once that is
satisfied the boiler and pump will stop so the radiators won't
get hot even if the room stat has opened the zone valve. That
surely can't be right?
A C-Plan system would have gravity HW and pumped CH and, if there
were a zone valve, this would be in the HW circuit and would have
microswitches. [See C-Plan in the link from my previous post] So
it ain't that.
How many wires are connected to the cylinder stat? Is it just an
on/off switch or a changeover. If the latter, where does the wire
go which becomes live when the stat is satisfied? If boiler water
continues to flow through the cylinder's internal coil after the
stat is satisfied, what stops the hot water from getting too hot
(assuming that the boiler flow temperature to the rads is higher
than the desired HW temperature)?
Sorry for all the questions, but I'm trying to understand how it
is supposed to work so that I can help with troubleshooting.
Ok. This is in several parts.
1. The plumber knew about the stuck pump nuts. He broke them
somehow (I wasn't there) and then removed the resin'ed remains
from the valves, along with the dead pump. Then he took the two
new valves, and knew how to separate the nuts from the valves.
Neat trick. These then went on the old valves, the new pump was
installed as normal. 2. When the pump was connected, and the timer
set to All on, the pump ran, and unlike the old one, has a
display, showing what appears to be a discharge pressure. This was
varying from 5 to 13 or so. I had checked the isolation valves,
and the tank feed valve, and they were all open. The boiler would
light, and then go out. 3. To cut a long story short, the whole
system was one big airlock. Bleeding air from the three radiators
in rotation resulted in the boiler finally staying on, and then
with the zone valve opened by the room 'stat, heat began to be
felt in the radiators. The pump was displaying a steady reading of
6.0 somethings. Being happy that the system was at least
operating, I left for home. Soon after I arrived here, 90 minutes
later, Simon called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat
before you mentioned it, but I checked my notes and that is
exactly how the system was, and is again, wired. It worked for
Simon all through last winter, and he had no reason to query it.
In a perfect world, a better way would be found, but "if it ain't
broke, don't fix it". 5. I don't see your problem with the current
Tank 'stat/pump/boiler arrangement. If the tank gets to setpoint,
it will shut the pump and boiler down, so I don't see runaway
happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring
Centre', aka J-Box, to improve and neaten the wiring to the
replacement timer, as its very small terminals do not enable good
tidy connections directly to it, whereas the old one had large
terminals. But the new J-box has equally small terminals, offering
little if any improvement. Back to the drawing board. I need to
source a J-Box with larger internal connectors.
7. The Boiler/pump/valve radiator layout is as I have described
it*. It does not conform to any of the published layouts. It is
closest to a 'C'-Plan, but with a different valve arrangement.
That is why I cannot name the Plan.
* The pump takes hot water from the boiler and sends it through the
-a-a tank heater coil, and back to the boiler. Just before the entry
to the boiler, there is a 'T' and the zone valve takes off from
that point to go to the radiators. That's it. I didn't design it.
I need a drink.
With the zone valve where you said it was, I am wondering whether
the water flow through the pump is in the direction you assume it
is.-a If you imagine the flow through the pump is in the opposite
direction you have (as near as dammit) a C-plan system.
I wondered about that but dismissed it because Davey's system appears
to be fully pumped - whereas C-Plan has gravity DHW - and C-Plan has
the zone valve in the HW - not CH - circuit *and* uses the valve's microswitch.
With the zone valve where you said it was, I am wondering whether
the water flow through the pump is in the direction you assume it
is.-a If you imagine the flow through the pump is in the opposite direction you have (as near as dammit) a C-plan system.
I wondered about that but dismissed it because Davey's system
appears to be fully pumped - whereas C-Plan has gravity DHW - and
C-Plan has the zone valve in the HW - not CH - circuit *and* uses
the valve's microswitch.
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Since I am thinking about replacing the ancient Randall with a modern
digital timer, I need to make sure that it has the same arrangement internally. Another day.
Big snip for brevity.
With the zone valve where you said it was, I am wondering whether
the water flow through the pump is in the direction you assume it
is.-a If you imagine the flow through the pump is in the opposite
direction you have (as near as dammit) a C-plan system.
I wondered about that but dismissed it because Davey's system
appears to be fully pumped - whereas C-Plan has gravity DHW - and
C-Plan has the zone valve in the HW - not CH - circuit *and* uses
the valve's microswitch.
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Since I am thinking about replacing the ancient Randall with a modern
digital timer, I need to make sure that it has the same arrangement
internally. Another day.
I followed the trail online which leads to the recommended replacement
for the existing analogue timer. Looking at the Danfoss information
online, it provides tons of information about how versatile the
programming is, but nothing to indicate if the same setup regarding the
DHW power is available. I e-mailed them, and ..........nothing
yet.
So I have a question for the electronics folks here. I have modified the wiring diagram to use a digital timer that separately powers the pump
and boiler when the valve microswitch is activated by the Room 'stat. My question is: Is there likely to be any harm done to the electronics in
the digital timer by feeding power from the microswitch to the terminal
which is the DHW control in the timer, ie backfeeding it from a
different location? It is still the same power, but feeding the load
side of the DHW terminal. I am concerned in case the electronic
component that usually makes the connection might not like power being applied to its load terminal but not its internal supply terminal. Maybe
it is not even a consideration, but maybe it is.
i will also ask Danfoss, once I have established communication with
them, but if anyone has any input, it would be most welcome.
On 10/01/2026 09:42, Davey wrote:
Big snip for brevity.
With the zone valve where you said it was, I am wondering whether
the water flow through the pump is in the direction you assume it
is.-a If you imagine the flow through the pump is in the opposite
direction you have (as near as dammit) a C-plan system.
I wondered about that but dismissed it because Davey's system
appears to be fully pumped - whereas C-Plan has gravity DHW - and
C-Plan has the zone valve in the HW - not CH - circuit *and* uses
the valve's microswitch.
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Except that you said that the tank stat turns off the boiler and pump
once it is satisfied. If that is true, the zone valve can open as
much as it likes but the radiators won't get hot if the boiler and
pump have been turned off.
But assuming that they *do* get hot by some mechanisn as yet
unexplained, there is nothing to stop the DHW from overheating when
the CH is on because water will still circulate round the HW circuit regardless of the tank stat.
That is encouraging. What I really need is a modern timer that has theSince I am thinking about replacing the ancient Randall with a
modern digital timer, I need to make sure that it has the same
arrangement internally. Another day.
I followed the trail online which leads to the recommended
replacement for the existing analogue timer. Looking at the Danfoss information online, it provides tons of information about how
versatile the programming is, but nothing to indicate if the same
setup regarding the DHW power is available. I e-mailed them, and ..........nothing yet.
In days of yore, when systems were common which had gravity HW and
pumped CH, programmers had an optional link which forced the boiler
on when there was a CH demand - but they probably don't do that now
because there must be very few gravity HW systems left.
So I have a question for the electronics folks here. I haveI don't see a problem with that. I have a similar situation - with an outside light which is controlled by a PIR. I have also wired a
modified the wiring diagram to use a digital timer that separately
powers the pump and boiler when the valve microswitch is activated
by the Room 'stat. My question is: Is there likely to be any harm
done to the electronics in the digital timer by feeding power from
the microswitch to the terminal which is the DHW control in the
timer, ie backfeeding it from a different location? It is still the
same power, but feeding the load side of the DHW terminal. I am
concerned in case the electronic component that usually makes the connection might not like power being applied to its load terminal
but not its internal supply terminal. Maybe it is not even a
consideration, but maybe it is. i will also ask Danfoss, once I
have established communication with them, but if anyone has any
input, it would be most welcome.
by-pass switch which sends power direct to the light so that I can
keep it on. The PIR doesn't seem to object to that. [As far as I am
aware, the PIR switches the mains directly rather than by means of a
relay].
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Except that you said that the tank stat turns off the boiler and pump
once it is satisfied. If that is true, the zone valve can open as
much as it likes but the radiators won't get hot if the boiler and
pump have been turned off.
But assuming that they *do* get hot by some mechanisn as yet
unexplained, there is nothing to stop the DHW from overheating when
the CH is on because water will still circulate round the HW circuit regardless of the tank stat.
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room 'stat
closes, and opens the valve. We don't know how long it takes, but the
next time the tank 'stat closes, firing the boiler and pump, there
is then circulation through the heating circuit.
On Sat, 10 Jan 2026 19:55:53 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Except that you said that the tank stat turns off the boiler and pump
once it is satisfied. If that is true, the zone valve can open as
much as it likes but the radiators won't get hot if the boiler and
pump have been turned off.
But assuming that they *do* get hot by some mechanisn as yet
unexplained, there is nothing to stop the DHW from overheating when
the CH is on because water will still circulate round the HW circuit
regardless of the tank stat.
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room 'stat
closes, and opens the valve. We don't know how long it takes, but the
next time the tank 'stat closes, firing the boiler and pump, there
is then circulation through the heating circuit. This continues until
the room 'stat is satisfied, and the system reverts to tank 'stat
control. We also don't know the hysteresis of the Room 'stat, it might
be quite small. I'll see if I can find anything on it.
The next time I am there, I will try to do some experiments. There is
no external indication of the state of the Room 'stat, so there is
nothing to bring a delay to anybody's attention, as long as the
temperature in the flat remains ok. It is certainly better than no heat
at all.
On 11/01/2026 09:38, Davey wrote:
On Sat, 10 Jan 2026 19:55:53 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Except that you said that the tank stat turns off the boiler and
pump once it is satisfied. If that is true, the zone valve can
open as much as it likes but the radiators won't get hot if the
boiler and pump have been turned off.
But assuming that they *do* get hot by some mechanisn as yet
unexplained, there is nothing to stop the DHW from overheating when
the CH is on because water will still circulate round the HW
circuit regardless of the tank stat.
The mechanism must be that: The tank 'stat brings the tank toSorry, but that ain't going to work! You *can't* rely on a demand for
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it takes,
but the next time the tank 'stat closes, firing the boiler and
pump, there is then circulation through the heating circuit. This
continues until the room 'stat is satisfied, and the system reverts
to tank 'stat control. We also don't know the hysteresis of the
Room 'stat, it might be quite small. I'll see if I can find
anything on it. The next time I am there, I will try to do some experiments. There is no external indication of the state of the
Room 'stat, so there is nothing to bring a delay to anybody's
attention, as long as the temperature in the flat remains ok. It is certainly better than no heat at all.
DHW to make the CH work - you could wait all day if you've got a well insulated tank of hot water and don't draw much off.
I've knocked up a schematic of how you would need to wire your
existing hardware to make it work (almost) correctly. See https://app.box.com/s/qq1u8olzksjl2mvibdiubj359i66u13r
My scheme uses the microswitch on the zone valve and turns on the
boiler and pump whenever either or both DHW and CH are demanding heat.
That still suffers from the problem that unless you run the boiler
flow temperature artificially low, the HW tank will continue to get
hotter than the tank stat set point whenever the CH is running.
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That should
be fairly trivial to do - and you would then, with the correct
wiring, have a fully fledged S-Plan system which would overcome the
problems which I highlighted above, and would enable your flat
occupant to live happily and cosily ever after!
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it takes,
but the next time the tank 'stat closes, firing the boiler and
pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the
CH, *either* of which will energise pump and boiler as their switch
outputs should be wired in parallel.
On Sun, 11 Jan 2026 11:43:13 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That should
be fairly trivial to do - and you would then, with the correct
wiring, have a fully fledged S-Plan system which would overcome the
problems which I highlighted above, and would enable your flat
occupant to live happily and cosily ever after!
I'll look at that schematic after lunch.
But consider this: There has never been a problem with the tank getting
too hot, and the system works fine.
On Sun, 11 Jan 2026 10:36:51 +0000
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it takes,
but the next time the tank 'stat closes, firing the boiler and
pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the
CH, *either* of which will energise pump and boiler as their switch
outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain't
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and money.
Taking your last point, my suggestion of using the microswitch to
operate the pump and boiler in parallel with the rank 'stat sounds
to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I can determine about its characteristics.
On 11/01/2026 12:16, Davey wrote:
On Sun, 11 Jan 2026 11:43:13 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That
should be fairly trivial to do - and you would then, with the
correct wiring, have a fully fledged S-Plan system which would
overcome the problems which I highlighted above, and would enable
your flat occupant to live happily and cosily ever after!
I'll look at that schematic after lunch.
But consider this: There has never been a problem with the tank
getting too hot, and the system works fine.
Since the whole thing is controlled by the tank stat, there wouldn't
be would there?
The problem will be a steaming hot water tank and therefore no
central heating at all....
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler
and pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the
CH, *either* of which will energise pump and boiler as their switch
outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain'tThe problem then becomes shutting down hot water supply or at least
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I
can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating
the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH
and DHW.
You cannot do it with just one. Unless its a three port device.
On Sun, 11 Jan 2026 12:29:01 +0000
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at least
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler
and pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the
CH, *either* of which will energise pump and boiler as their switch
outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain't
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I
can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating
the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH
and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is on, so
is the DHW.
On 11/01/2026 12:39, Davey wrote:
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its been
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at least
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler
and pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the
CH, *either* of which will energise pump and boiler as their switch
outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain't
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I
can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating
the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH
and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is on, so
is the DHW.
set up so that the tank never in fact is hot enough by limiting the
boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even usual
way to do things.
On 11/01/2026 12:45, The Natural Philosopher wrote:
On 11/01/2026 12:39, Davey wrote:
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the
boiler and pump, there is then circulation through the heating
circuit.
You should have two motorized valves, one for the tank, one for
the CH, *either* of which will energise pump and boiler as
their switch outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it
ain't broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what
I can determine about its characteristics.
least limiting the boiler heat output to - say - 60-#C to avoid
overheating the hot water cylinder.
The point to having two MVs is to allow *independent* operation
of CH and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is
on, so is the DHW.
been set up so that the tank never in fact is hot enough by
limiting the boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even
usual way to do things.
I've not been following this thread particularly ... but isn't the OP describing a 'C plan' arrangement?
<http://www.home-heating-systems-and-solutions.com/central-heating-design.html#cplan>
On 11/01/2026 09:38, Davey wrote:
On Sat, 10 Jan 2026 19:55:53 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
I think I have solved the mystery. The timer does not offer
DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot
water is already running. Simple!
Except that you said that the tank stat turns off the boiler and
pump once it is satisfied. If that is true, the zone valve can
open as much as it likes but the radiators won't get hot if the
boiler and pump have been turned off.
But assuming that they *do* get hot by some mechanisn as yet
unexplained, there is nothing to stop the DHW from overheating when
the CH is on because water will still circulate round the HW
circuit regardless of the tank stat.
The mechanism must be that: The tank 'stat brings the tank toSorry, but that ain't going to work! You *can't* rely on a demand for
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it takes,
but the next time the tank 'stat closes, firing the boiler and
pump, there is then circulation through the heating circuit. This
continues until the room 'stat is satisfied, and the system reverts
to tank 'stat control. We also don't know the hysteresis of the
Room 'stat, it might be quite small. I'll see if I can find
anything on it. The next time I am there, I will try to do some experiments. There is no external indication of the state of the
Room 'stat, so there is nothing to bring a delay to anybody's
attention, as long as the temperature in the flat remains ok. It is certainly better than no heat at all.
DHW to make the CH work - you could wait all day if you've got a well insulated tank of hot water and don't draw much off.
I've knocked up a schematic of how you would need to wire your
existing hardware to make it work (almost) correctly. See https://app.box.com/s/qq1u8olzksjl2mvibdiubj359i66u13r
My scheme uses the microswitch on the zone valve and turns on the
boiler and pump whenever either or both DHW and CH are demanding heat.
That still suffers from the problem that unless you run the boiler
flow temperature artificially low, the HW tank will continue to get
hotter than the tank stat set point whenever the CH is running.
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That should
be fairly trivial to do - and you would then, with the correct
wiring, have a fully fledged S-Plan system which would overcome the
problems which I highlighted above, and would enable your flat
occupant to live happily and cosily ever after!
On 11/01/2026 12:45, The Natural Philosopher wrote:
On 11/01/2026 12:39, Davey wrote:I've not been following this thread particularly ... but isn't the OP describing a 'C plan' arrangement?
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its been
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at least
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler >>>>>>> and pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the >>>>>> CH, *either* of which will energise pump and boiler as their switch >>>>>> outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain't
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I
can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating
the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH
and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is on, so
is the DHW.
set up so that the tank never in fact is hot enough by limiting the
boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even
usual way to do things.
<http://www.home-heating-systems-and-solutions.com/central-heating- design.html#cplan>
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That should
be fairly trivial to do - and you would then, with the correct
wiring, have a fully fledged S-Plan system which would overcome the
problems which I highlighted above, and would enable your flat
occupant to live happily and cosily ever after!
On 11/01/2026 12:45, The Natural Philosopher wrote:
On 11/01/2026 12:39, Davey wrote:I've not been following this thread particularly ... but isn't the OP describing a 'C plan' arrangement?
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its been
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at least
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to
temperature, and shuts off the pump and boiler. Later, the Room
'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler >>>>>>> and pump, there is then circulation through the heating circuit.
You should have two motorized valves, one for the tank, one for the >>>>>> CH, *either* of which will energise pump and boiler as their switch >>>>>> outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it ain't
broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I
can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating
the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH
and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is on, so
is the DHW.
set up so that the tank never in fact is hot enough by limiting the
boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even
usual way to do things.
<http://www.home-heating-systems-and-solutions.com/central-heating-design.html#cplan>
On 11/01/2026 13:16, jkn wrote:
On 11/01/2026 12:45, The Natural Philosopher wrote:There was no mention of automatic by pass...
On 11/01/2026 12:39, Davey wrote:I've not been following this thread particularly ... but isn't the OP
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at least
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank toYou should have two motorized valves, one for the tank, one for the >>>>>>> CH, *either* of which will energise pump and boiler as their switch >>>>>>> outputs should be wired in parallel.
temperature, and shuts off the pump and boiler. Later, the Room >>>>>>>> 'stat closes, and opens the valve. We don't know how long it
takes, but the next time the tank 'stat closes, firing the boiler >>>>>>>> and pump, there is then circulation through the heating circuit. >>>>>>>
But there is only one, and the system appears to work. "If it ain't >>>>>> broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution for a
problem that has never existed is a waste of time, energy, and
money. Taking your last point, my suggestion of using the
microswitch to operate the pump and boiler in parallel with the
rank 'stat sounds to have the same effect as what you propose.
I have found the model number of the room 'stat, I will see what I >>>>>> can determine about its characteristics.
limiting the boiler heat output to - say - 60-#C to avoid overheating >>>>> the hot water cylinder.
The point to having two MVs is to allow *independent* operation of CH >>>>> and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does not
enable independent operation of CH and DHW anyway, if the CH is on, so >>>> is the DHW.
been set up so that the tank never in fact is hot enough by limiting
the boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even
usual way to do things.
describing a 'C plan' arrangement?
<http://www.home-heating-systems-and-solutions.com/central-heating-
design.html#cplan>
On Sun, 11 Jan 2026 11:43:13 +0000
Roger Mills <mills37.fslife@gmail.com> wrote:
As TNP has said, the proper way to do it would be to get an
additional zone valve and insert it into the HW circuit. That should
be fairly trivial to do - and you would then, with the correct
wiring, have a fully fledged S-Plan system which would overcome the
problems which I highlighted above, and would enable your flat
occupant to live happily and cosily ever after!
He lived cosily and happily through the whole of last winter, and
now appears to be doing so in this one as well.
Installing a valve would not be too difficult, but I have seen no
compelling reason to do so. Theoretical, yes, but theoretically the HW
system shouldn't work, but it does, and very well.
I think I have a dead zone valve. If I apply power, there is no
movement of the little manual operator tit. I can move this across, and
there is the expected resistance as it moves. I can hook it in place,
or let go, and it spring returns to the closed position.
Should the lever move when the valve is energised, as I believe it
should?
Don't say 'does it let water through?', we are not at that stage yet.
This is a 1986 system, that appears to have had failure of most of its ancient components, and I am debugging or replacing them one by one.
And this is 75 miles from home!
On 22/12/2025 17:53, Davey wrote:
I think I have a dead zone valve. If I apply power, there is no
movement of the little manual operator tit. I can move this across,
and there is the expected resistance as it moves. I can hook it in
place, or let go, and it spring returns to the closed position.
Should the lever move when the valve is energised, as I believe it
should?
Don't say 'does it let water through?', we are not at that stage
yet. This is a 1986 system, that appears to have had failure of
most of its ancient components, and I am debugging or replacing
them one by one. And this is 75 miles from home!
An old thread I know.
A energised motor runs warm. With the heating on and cold pipes it
should be obvious. If cold then I would check power to the motor
before condemning it.
Motors can replaced on their own without the need for a system drain
down and refill.
On 11/01/2026 19:05, The Natural Philosopher wrote:
On 11/01/2026 13:16, jkn wrote:
On 11/01/2026 12:45, The Natural Philosopher wrote:There was no mention of automatic by pass...
On 11/01/2026 12:39, Davey wrote:I've not been following this thread particularly ... but isn't the
On Sun, 11 Jan 2026 12:29:01 +0000BUT the CH will shut down when the tank is hot enough. Unless its
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 12:22, Davey wrote:
On Sun, 11 Jan 2026 10:36:51 +0000The problem then becomes shutting down hot water supply or at
The Natural Philosopher <tnp@invalid.invalid> wrote:
On 11/01/2026 09:38, Davey wrote:
The mechanism must be that: The tank 'stat brings the tank to >>>>>>>> temperature, and shuts off the pump and boiler. Later, the
Room 'stat closes, and opens the valve. We don't know how
long it takes, but the next time the tank 'stat closes,
firing the boiler and pump, there is then circulation
through the heating circuit.
You should have two motorized valves, one for the tank, one
for the CH, *either* of which will energise pump and boiler
as their switch outputs should be wired in parallel.
But there is only one, and the system appears to work. "If it
ain't broke, don't fix it" is a very useful maxim.
Trying to understand it, yes, but trying to find a solution
for a problem that has never existed is a waste of time,
energy, and money. Taking your last point, my suggestion of
using the microswitch to operate the pump and boiler in
parallel with the rank 'stat sounds to have the same effect as
what you propose. I have found the model number of the room
'stat, I will see what I can determine about its
characteristics.
least limiting the boiler heat output to - say - 60-#C to avoid
overheating the hot water cylinder.
The point to having two MVs is to allow *independent* operation
of CH and DHW.
You cannot do it with just one. Unless its a three port device.
But as I say, this has never been a problem. And the timer does
not enable independent operation of CH and DHW anyway, if the CH
is on, so is the DHW.
been set up so that the tank never in fact is hot enough by
limiting the boiler outflow temperature.
If it works, fine, but don't argue that it is the correct or even
usual way to do things.
OP describing a 'C plan' arrangement?
<http://www.home-heating-systems-and-solutions.com/central-heating-
design.html#cplan>
Indeed. But since the boiler is 50 years old, it almost certainly has
a heavy cast iron heat exchanger and large water capacity, so it
doesn't suffer fron overheating when it's turned off with no over-run
water flow. There's pretty certainly no pump over-run because the
pump appears to be wired in parallel with the boiler.
If the boiler is ever replaced by a modern one with a low volume
aluminium heat exchanger, and a proper S-Plan control installed,it
will probably then need to have pump over-run and an auto by-pass.
In days of yore, when systems were common which had gravity HW and
pumped CH, programmers had an optional link which forced the boiler on
when there was a CH demand - but they probably don't do that now because there must be very few gravity HW systems left.
On 10/01/2026 19:55, Roger Mills wrote:
In days of yore, when systems were common which had gravity HW and
pumped CH, programmers had an optional link which forced the boiler on
when there was a CH demand - but they probably don't do that now
because there must be very few gravity HW systems left.
I have got one.-a The HW tank is on a platform half a metre above the top
of the floor mounted boiler so the gravity pipework is quite short. When
the Programmer HW setting has the HW function On, the HW tank thermostat decides whether the zone valve is open or closed, and the zone valve microswitch allows the boiler to fire up when the zone valve is open.
When the Programmer CH setting has the CH function On the CH room
thermostat decides whether the pump runs and if the pump runs then the
same circuit allows the boiler to fire up.
The programmer is basically an electric clock that has 2 ons and 2 offs (alternately, on/off/on/off) that I set to the times I want.-a Then there
is a slide switch for each of CH and HW, so for each I can choose
between Always On, or On at the first time and Off at the last time (=on
all day), or On then Off then On then Off for being on twice a day with
Off for the time between, or Off permanently.-a There is also a frost thermostat wired in which overrides the timeswitch settings to make the
CH run whenever the temperature gets down to the frost temperature.
It took a bit of thinking and a large sketch to work out what had to be connected to what, and it all worked after I wired it up.-a My father and
my younger brother were both qualified electricians so from an early age
I have always known how to wire things up properly.
I had bought a long strip of screw-onto-the-wire connectors which I
mounted in a plastic box, and it made connecting thermostats to the
things that functioned when satisfied or unsatisfied very easy.-a I
labelled the sections of connectors with "mains", "HW", "Zone", "CH"
before I screwed the lid on the plastic box so that if I ever sell the house, the buyer will have some idea of which wires do what.
In days of yore, when systems were common which had gravity HW and
pumped CH, programmers had an optional link which forced the boiler on
when there was a CH demand - but they probably don't do that now because there must be very few gravity HW systems left.
I have a relay in my wiring centre so that both the C/H and DHW outputsSo I have a question for the electronics folks here. I have modified the
wiring diagram to use a digital timer that separately powers the pump
and boiler when the valve microswitch is activated by the Room 'stat. My
question is: Is there likely to be any harm done to the electronics in
the digital timer by feeding power from the microswitch to the terminal
which is the DHW control in the timer, ie backfeeding it from a
different location? It is still the same power, but feeding the load
side of the DHW terminal. I am concerned in case the electronic
component that usually makes the connection might not like power being
applied to its load terminal but not its internal supply terminal. Maybe
it is not even a consideration, but maybe it is.
i will also ask Danfoss, once I have established communication with
them, but if anyone has any input, it would be most welcome.
I don't see a problem with that.
On 13/01/2026 01:33, Indy Jess John wrote:
On 10/01/2026 19:55, Roger Mills wrote:Yes, indeed - there will still be a few such systems in existence - just
In days of yore, when systems were common which had gravity HW and
pumped CH, programmers had an optional link which forced the boiler
on when there was a CH demand - but they probably don't do that now
because there must be very few gravity HW systems left.
I have got one.-a The HW tank is on a platform half a metre above the
top of the floor mounted boiler so the gravity pipework is quite
short. When the Programmer HW setting has the HW function On, the HW
tank thermostat decides whether the zone valve is open or closed, and
the zone valve microswitch allows the boiler to fire up when the zone
valve is open. When the Programmer CH setting has the CH function On
the CH room thermostat decides whether the pump runs and if the pump
runs then the same circuit allows the boiler to fire up.
The programmer is basically an electric clock that has 2 ons and 2
offs (alternately, on/off/on/off) that I set to the times I want.
Then there is a slide switch for each of CH and HW, so for each I can
choose between Always On, or On at the first time and Off at the last
time (=on all day), or On then Off then On then Off for being on twice
a day with Off for the time between, or Off permanently.-a There is
also a frost thermostat wired in which overrides the timeswitch
settings to make the CH run whenever the temperature gets down to the
frost temperature.
It took a bit of thinking and a large sketch to work out what had to
be connected to what, and it all worked after I wired it up.-a My
father and my younger brother were both qualified electricians so from
an early age I have always known how to wire things up properly.
I had bought a long strip of screw-onto-the-wire connectors which I
mounted in a plastic box, and it made connecting thermostats to the
things that functioned when satisfied or unsatisfied very easy.-a I
labelled the sections of connectors with "mains", "HW", "Zone", "CH"
before I screwed the lid on the plastic box so that if I ever sell the
house, the buyer will have some idea of which wires do what.
not very many!
Sounds like you've got a C-Plan system, or something very close to one.
How long ago did you install it?
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