My central heating has a time switch which turns the radiators and water on and off at the set times. i have noticed that when the timer has switched off the radiators sometimes the boiler fires up on its own and the thermostat light is on but although it clicks it does not shut down the heating and only way round this is to turn off electric at the boiler and then put it back on again, can anyone tell me where the faults lies, is it the thermostat, the timer or the boiler? 
