My heating system seems to cause the radiators to heat up when only the DHW setting is on. My system consists of a condensing boiler (Greenstar 29HE Conventional), fully pumped with two isolating valves, frost protection thermostat and auto-bypass valve.
I do not think the frost stat has anything to do with the problem since this overides all timer settings to switch the boiler on and the problem occurs only when DHW is on.
I suspected the auto-bypass valve but setting this at its maximum setting has not cured the problem.
I have checked the CH isolating valve to see if its opening but that does not seem to be the case yet nearly all the radiators are heating up, some quite considerably.
Any suggestions before we melt in the heat.
Ta1 Tricky Dicky