i have ravenheat he 85t boiler, i have noticed 3 to 3 times a wee the raditors seem to come on by them selfs, even tho the boiler is just switched to on the water mode, the thermostate is off, there is no auto timeing set or nothing, but they still come on, and then i have to reset the boiler everytime for them to go of, and alsp realised when the radiators come on the temp needle slightly goes up and the red fire light starts to flier

ahmed, July 2010

your hot water thermostat is faulty and the boiler to protect itself is running the pump to remove heat from the heat exchanger

serpen66, July 2010

I don't know your particular boiler, but I would suggest one of two things:
1: Electrical fault in internal/external controls allowing heating to come on (unlikely but possible).

2: Your boiler has a water 'preheat' function, this (as it suggests) pre-heats the domestic heat exchanger so the hot water is about as 'instant' as it can be.

If this is the case (likely suspect), then the boiler diverter valve would be at fault, it could be allowing the water designed to pre-heat the domestic water to 'leak' through the diverter into the heating system thus never satisfying the domestic pre-heat, and making the radiators hot.

Carefree, July 2010