very easy this one my friend plate heat exchanger blocked with limescale or debris hot water does not get away from the boiler quick enough and sensor kicks in boiler will fire then go out fire then go out repeatedly little tip the het exchangers for the baxi combis are 16 or 24 plate if you need a replacment go for the 24 plate and you will see a vast improvement of your hot water at your taps shower etc drain boiler of dhw turn off cw supply two screws 4 washers ,sometimes you dont need to rplace the washers use same again tighten up refill jobs a good un
byron, October 2010
