my sime 80e boiler has the heating on all the time. the only way to turn it off is at the mains or to turn the selector switch to off which means i have no hot water. I have checked the Frost stat and the timeclock and are both working fine but have a permenant live at the switched side of the clock even in summer mode.

Dave O'Brien, August 2010

most likely i would say is the pin on the opening for the central heating flow switch is most likely stuck in the n position most likely need a service kit as debris or worn parts inside the valve

kash, August 2010