We have a fifteen year old combi worcester Bosch 230 boiler that was bringing the heating on after water had been used, it wasnt simply disipating the heat in the boiler it would light up the demand light and fire the boiler until all the system was hot. sometimes it would then switch off other times it would need a manual switching off at the mains.( this was in June) British gas have changed both of the control boards and finally the three way eletrical on/off/hotwater switch. All seemed ok, but now it is also doing the above, if we use hot water say at 7.00 am, plus it is also bringing the heating on when the timer is set to off namely middle of the night, once again the demand light is showing as on and cannot be turned off without switching off at mains. There is no room stat or frost stat fitted it controls the temperature on the return water temperature. Any ideas before i call B/Gas at more cost.