Central heating doesnt switch off

[jpm321]

Hi

I have a potterton suprima boiler, when the thermostat in the hall swiches the heating on the light comes on on the 3 point valve and the motorised arm indicates the valve has moved and the heating comes on as it should

but when the house is at desired temp the thermostat switches off, the light goes off on the 3 point valve but the motorised arm doesnt move so heating stays on
If i power off the boiler circuit the motorised valve moves and the heating goes off
this is the only way i can turn the heating OFF

on is ok

I did remove the 3 point valve and turned thermostat on/off several times watching the motor move

Im not sure if i need to replace the boiler curcuit board or the 3 point valve, not convinced its the 3 point valve as this works when its in my hand

any ideas

 

[jpm321]

 

[D_Hailsham]

when the house is at desired temp the thermostat switches off, the light goes off on the 3 point valve but the motorised arm doesnt move so heating stays on

Do you mean the metal lever in the slot at the side, marked Auto/Manual does not move? If so, this is no indication that the valve has moved. It is simply away of holding the valve open when refilling the CH system (the lever is clipped into the Man slot).

Do the Boiler and Pump stop when the Room stat turns off?

If i power off the boiler circuit the motorised valve moves and the heating goes off. this is the only way i can turn the heating OFF

Here is the wiring diagram for a Y-plan, which is what you will have with a 3-port valve. You should check this first. (the pump may be wired directly to the boiler)

 

[jpm321]

the Pump doesn't seem to go off at all, its constantly on

the room thermostat turns the light off on the 3 way valve but the pump stays on

even if i power down/up the boiler pumps stays on

James

 

[jpm321]

just had a quick look and my wireing isnt exactly the same as this diagram
should my wireing eactly match theis diagram

cant see what wires are my boiler and room thermstat all seem y/r/b

 

[D_Hailsham]

the Pump doesn't seem to go off at all, its constantly on

the room thermostat turns the light off on the 3 way valve but the pump stays on

even if i power down/up the boiler pumps stays on

The pump on a Potterton Suprima is wired directly to the Boiler and controlled by the over-run thermostat. This means that, when the boiler stops firing, the pump will continue running for several minutes to cool the heat exchanger down.

If the pump never stops, then, usually, the overheat thermostat is faulty. But you say the pump stays on when you power the boiler down. How are you doing this? Are you just turning the boiler's own switch or the time-switch to OFF or are you turning the whole heating installation off at the wall switch (usually near the boiler or in the airing cupboard with the MV etc). If the pump continues when you switch off at the main wall switch, then there is something wrong with the wiring. But if it continues when you switch off at the boiler/timeswitch then the over-run stat is faulty.

The wiring may not be exactly the same as the diagram. For example the pump will be wired directly to the boiler (though this may be via the connection strip if the pump is not inside the boiler).

The important thing is that the timeswitches, thermostats and the 3-way valve are wired correctly; i.e. when you turn the heating on and the thermostat up, the white wire of the valve is alive, etc.

 

[jpm321]

My mistake,

the pump only stops when i switch the mains off for the boiler

the white wire is constantly live when the room therm is on and off

where is the over-run stat , anything i can test there?

 

[baxpoti]

the pump only stops when i switch the mains off for the boiler

If pump is correctly wired to the boiler, PCB needs replacing.

 

[Timmyturtle]

Being a Suprima....Do Potterton replace these pcb`s free of charge??
or is it a set price since the Watchdog programme??

Just in case i get another one

 

[D_Hailsham]

the white wire is constantly live when the room therm is on and off

That's wrong

The white wire should only be live when the Room stat is calling for heat.

Disconnect the white wire and check if it is still live when the room stat is turned down. If so, the room stat is faulty.