The problem is with the hot tap water side of the boiler, (the central heating works fine all the time). When a hot water tap is turned on the boiler fires up, (or increases the gas if the central heating is already on), then runs for 2 or 3 seconds and then turns the gas, (or extra gas), off. It then cycles through this by starting up, (or increasing the gas), and stopping, (or reducing to just the central heating amount of gas).

So in essence once the water is turned on and the boiler fires up there is something monitoring the system and shutting down the tap water heating part only. Any suggestions would be greatly appreciated.

Ross, October 2006

how do i set my timer on my boiler

mrs s crawley, November 2012

fan won't work every summer have this problem

sam, June 2009

the rubber diaphragm in the diverter valve has deteriorated and is letting water pressure escape past the diaphragm and is not maintaining enough pressure on the microswitches. The initial surge of pressure is enough to initiate ignition for the hot water but after a few seconds line pressure normalises and the diaphragm relaxes, breaking the electrical circuit.

Josh Hooker, August 2008