Boiler won't turn on heating.

[Rob_Quads]

I've got a Glow-worm Fuelsaver 35F boiler (i think) which has started to misbehave every so often. The problem occurs if the heating tries to turn on on its own. Nothing happens. The room thermostat is showing live so its feeding power accordingly but nothing. The gas not turned on either.
If you then tell it to turn on the water the boiler will fire up and the heating will also operate accordingly

To fix it I have to pull the power from the boiler and then switch it back on again at the fuse box. After this its all fine again.

Its very random as to when it can do it, it was weeks ago before it did it last but then it did it a couple times in a week.

I have recently changed the room thermostat and timer module too neither of which affected this problem.

 

[D_Hailsham]

Do you have a mid-position valve, as in the pic? If so that is most likely to be the culprit.

View media item 5946
It will usually be near the hot water cylinder.

 

[Rob_Quads]

yeah I do. It looks like its moving around when i select the heating but not fully.

Would that not working stop the boiler kicking in?

 

[D_Hailsham]

Read Mid-position valve working and Diagnostics and you should learn all you need to know to diagnose the cause of your problem.