I have an old Thorn Apollo boiler, a Randall 4033 timer and a 3 wire
thermostat. Until now this system has been very reliable but now the
radiators now only heat up when the boiler is heating the hot water tank.

The live connection on the room thermostat is live and the switched
connection becomes live when I turn the thermostat up but neither the
boiler nor circulating pump come on. The boiler is in my garage and I
have a frost prevention thermostat - if I turn this up the boiler and
circulating pump come on and the radiators heat up but the boiler
doesn't seem to respond to the main thermostat.

Any ideas what's wrong and how to fix it? I would be grateful for any
suggestions.

Thanks,

Gareth.

On 07/11/2017 23:28, Gareth wrote:
I have an old Thorn Apollo boiler, a Randall 4033 timer and a 3 wire
thermostat. Until now this system has been very reliable but now the
radiators now only heat up when the boiler is heating the hot water tank.

The live connection on the room thermostat is live and the switched
connection becomes live when I turn the thermostat up but neither the
boiler nor circulating pump come on.Â* The boiler is in my garage and I
have a frost prevention thermostat - if I turn this up the boiler and
circulating pump come on and the radiators heat up but the boiler
doesn't seem to respond to the main thermostat.

Any ideas what's wrong and how to fix it?Â* I would be grateful for any
suggestions.

Thanks,

Gareth.

I suggest that you make sure than any zone valve that you may have is
working properly and is not stuck.


--
Michael Chare

On Tue, 7 Nov 2017 23:56:43 +0000
Michael Chare wrote:

On 07/11/2017 23:28, Gareth wrote:
I have an old Thorn Apollo boiler, a Randall 4033 timer and a 3
wire thermostat. Until now this system has been very reliable but
now the radiators now only heat up when the boiler is heating the
hot water tank.

The live connection on the room thermostat is live and the switched
connection becomes live when I turn the thermostat up but neither
the boiler nor circulating pump come on.Â* The boiler is in my
garage and I have a frost prevention thermostat - if I turn this up
the boiler and circulating pump come on and the radiators heat up
but the boiler doesn't seem to respond to the main thermostat.

Any ideas what's wrong and how to fix it?Â* I would be grateful for
any suggestions.

Thanks,

Gareth.

I suggest that you make sure than any zone valve that you may have is
working properly and is not stuck.



Agreed. it sounds like a valve not making the limit switch, either
because the valve is stuck, or the switch is faulty.
Remember that there is probably a zone valve controlled by the tank
thermostat, depending on the arrangement.

--
Davey.

Got to agree that it is probably a faulty zone valve. If you need heat whilst waiting repair you should be able to manually open the valve by moving a lever on the motor housing as long as it not the valve itself that is stuck. Manually opening the valve means you will not have any temperature control except for those radiators fitted with TRVs but the boiler stat will continue to control water temp and by turning any manual valves down you should be able to ensure you do not get runaway temp rises. This all assumes the switch in the zone valve which switches on the pump is not what is at fault. A good indicator of a faulty switch is the motor turning but the pump not switching on.

Richard

On 08/11/2017 09:06, Tricky Dicky wrote:
Got to agree that it is probably a faulty zone valve. If you need heat whilst waiting repair you should be able to manually open the valve by moving a lever on the motor housing as long as it not the valve itself that is stuck. Manually opening the valve means you will not have any temperature control except for those radiators fitted with TRVs but the boiler stat will continue to control water temp and by turning any manual valves down you should be able to ensure you do not get runaway temp rises. This all assumes the switch in the zone valve which switches on the pump is not what is at fault. A good indicator of a faulty switch is the motor turning but the pump not switching on.

Richard

I have just had two fail myself. I think usually if not always you can
prise the motor from off the valve. You can then see if the motor
switches according to the central heating and hot water demands. You can
also check that you can twist the valve off and on quite easily with
your fingers. A stiff valve can lead to the motor failing. Much easier
to change the motor than the valve body! In my case it was the motors
that had failed. By taking the motor apart I was able to disconnect the
cable from old motor and then attach it to the new one.

--
Michael Chare

On 08/11/2017 09:06, Tricky Dicky wrote:
Got to agree that it is probably a faulty zone valve. If you need heat whilst waiting repair you should be able to manually open the valve by moving a lever on the motor housing as long as it not the valve itself that is stuck. Manually opening the valve means you will not have any temperature control except for those radiators fitted with TRVs but the boiler stat will continue to control water temp and by turning any manual valves down you should be able to ensure you do not get runaway temp rises. This all assumes the switch in the zone valve which switches on the pump is not what is at fault. A good indicator of a faulty switch is the motor turning but the pump not switching on.

Richard

Thanks for all the replies.

It was the switch in the zone valve. The valve seems to move all the
way across but the switch wasn't quite closing. I've bent the springy
level on the switch a little bit and the boiler and pump now respond to
the room thermostat and still respond to the cylinder thermostat.

Thanks to everyone who replied.

Gareth

On Wed, 8 Nov 2017 22:55:14 +0000
Gareth wrote:

On 08/11/2017 09:06, Tricky Dicky wrote:
Got to agree that it is probably a faulty zone valve. If you need
heat whilst waiting repair you should be able to manually open the
valve by moving a lever on the motor housing as long as it not the
valve itself that is stuck. Manually opening the valve means you
will not have any temperature control except for those radiators
fitted with TRVs but the boiler stat will continue to control water
temp and by turning any manual valves down you should be able to
ensure you do not get runaway temp rises. This all assumes the
switch in the zone valve which switches on the pump is not what is
at fault. A good indicator of a faulty switch is the motor turning
but the pump not switching on.

Richard

Thanks for all the replies.

It was the switch in the zone valve. The valve seems to move all the
way across but the switch wasn't quite closing. I've bent the
springy level on the switch a little bit and the boiler and pump now
respond to the room thermostat and still respond to the cylinder
thermostat.

Thanks to everyone who replied.

Gareth

Glad it worked out ok.

--
Davey.