I have a Worcester 350 combi-boiler with a repeatable problem that the service guy can't seem to fix! After about 2-3hrs of being on, the central heating cycle of the boiler stops and the pipes go cool. The pump still pumps the water round, but it's not firing up to heat it. Have replaced the temperature sensor and a variety of other things.
I found I could temporarily resolve it: power the boiler off and on, or press the reset-buttons (day and min) on the front panel to reset the clock to 12:00am (if it got scrambled this is what it says to do). This pretty much always works. For another 2 hours.
What do I need to replace to fix this?
Mike