Flame-out on CH but OK on HW

[martca]

I have a pressurised system supplied by a Potterton Suprema. When calling for HW it lights and burns well but when calling for CH it lights for 5 secs and then goes out. Can anyone help please.

 

[gas4you]

Check your zone valve/s and programmer and room stat are ok.

The boiler does not know whether it is being asked for ch or dhw.

 

[martca]

Thanks Dave - I know the stat is ok because when the CH is on at the programmer and I turn the stat up it will click and the boiler will light but then goes straight out. The radiators will also all warm up normally but only when the HW is on and calling i.e. after the shower has been used.

 

[snb]

As dave has said check the zone valve/s Normally needs new syncron motor as it's lost it's ability to move the valve far enough to activate the microswitch