Got Hot water but no heating

[JamesR]

I have a Potterton 28 performa. I am getting hot water as the pilot light is coming on, but won't light to heat the radiators. Any ideas?

 

[cross thread]

START WITH THE BASICS,CLOCK ON,ROOM STAT TURNED UP,BOILER SWITCH TURNED TO HEATING .

 

[JamesR]

Thanks for that. I have turned temp up full, turned boiler off and on, put boiler onto timer and also constant. Tried to reset the boiler. No joy. Hot water is fine. The pump starts and pilot lights no problem.

 

[JamesR]

Well it seems to be working today. It wasn't when I got up this morning but when I got home tonight it had switched on even though I hadn't changed a thing. Weird or what?

 

[MANDATE]

Do you have a 3 port mid position valve in your system? If so you may find the actuator does not function correctly. Sometimes you cannot get CH to work alone, but it operates ok when there is demand for both CH and HW. The reason it works in this situation is because the boiler is powered from a different source, but as soon as HW is satisfied and the valve moves, the source of power is changed and if that source is faulty then you have no CH.
Power source for HW is from cylinder stat.
Power source for HW/CH is from cylinder stat
Power source for CH is from Mid position valve (orange wire)
If you have a 3 port valve this could explain why you think it seems to be working.

 

[namsag]

mandate its a combi. Sounds like yet again a boiler defies all logic and decides to work with no one touching it

 

[JamesR]

Well it's gone again. No heating but hot water is fine. It stopped working again as suddenly as it started. Ay ideas? Thanks