Please can somone help with the following problem: -

I have a potterton 80 boiler and all of a sudden the central heating won't work
properly. It starts up but goes off after about 25 seconds. The pilot light
then extinguishes. The hot water is fine though? No problems with that.

Somebody mentioned that it might be the divertor valve? Are these expensive to
buy. If so, is it posssible to remove the existing valve, clean it up and
replace?

Perhaps it isn't the valve atall. I would be grateful of any help anybody can
offer to me.

Thanks

K