No Central Heating but Hot Water is OK. HELP!!!

[smandir]

I have a Vaillant Combi, the Pilot light is lit and hot water works fine, but when the heating is switched on the boiler is attempting to fire up but keeps failing. Any suggestions?

 

[kevplumb]

servo valve aint coming right off

 

[smandir]

Does that mean i need a whole new Servo valve? If so how much should this cost in Uk £

 

[kevplumb]

might not be the servo valve the pin that operates it has a habit of sticking
might just need a clean and bit of lube

 

[smandir]

When i turned the heating on it fired up and worked until it reached the correct temp then it fails to automatically fire again. It also stops working if someone uses the hot water. Does this still sound like the servo valve?