Please help, Vaillant CH problem

[Don2]

Model VCW GB 242 EH, about 15 years old, DHW works well, CH working but not warm enough.

boiler fires when CH switched on, blue flame but stays low only about an inch tall and goes off when temperature reaches 65 degrees c on the meeter. Refires when the temperature drops down to 40 degrees. Flame stay on for only about 50 secs by which time the temperature reaches 65c. The radiaters stayes lukewarm.

 

[chrishutt]

Sounds like a problem with circulation through radiator circuits. Could be restriction caused by sludge or air. Lots of threads dealing with this. Behaviour of boiler sounds OK given very restricted circulation on CH.

 

[Don2]

Thanks Chrishutt

I shall flush and bleed the system over the weekend. Thanks again

Don2