great ricky, thanks for the advice. i already checked fan and it looks like its working ok. think it could be the flue pressure diff switch, as it seemed to do an exaggerated version of the fault when i disconnected one of its pipes. will try to clean it out, or replace it. do you know of anyone good for servicing boilers in london area? i've had some trouble with cowboys who don't have a clue on repairs but are very good at giving quotes for a new boiler!
tomh
August 2009