The HW suppy is intermittent. From a cold start the fault indicator sometimes shows a sensor/overheating fault but if you leave it for a few hours it works ok, some days no fault all day. Engineer suggested that it might be hardness in water collected in boiler (live in an area of very hard water). When the fault occurs if I turn on Central Heating after a while the HW works ok. Any ideas.

Mr M watch, October 2006

the heating engineer changed to hot water sensor / thermostat...all ok now,

M Watch, December 2006

always worth changing the diaphragm ,if it is indicating overheating then the heat exchangers might be restricting the flow of water due to sludge or limescale, remove the domestic heat exchanger and have a look down the inlet and outlet it doesnt need much to slow the flow down but cleaning them properly is a tricky job ,you really need to pump warm descaling acid around the heat exchanger,if your not sure you can tackle this job calling a plumber could actually save you money

roy(service engineer), October 2006