I have an old baxi boiler about 15years it works fine and heats radiators and water no problem but recently when it is on it continually fires every 15seconds ! What can cause this and is it costing more it is annoying as is noisy
Thank you in advance of any ideas

L payne, November 2013

....or the air pressure switch may be dropping in and out for some reason

Gas Safe Engineer in West Yorkshire, November 2013

It sounds like it may be related to the flame detection process which may mean anything from a good service and cleaning the probe, to a new PCB. It won't cost more to run particularly, but it is putting the boiler under more strain by continually opening and shutting the gas valve. Time to get a registered engineer in.

Gas Safe Engineer in West Yorkshire, November 2013