Hi hope someone can help my worcester 18 ri boiler is now 18 months old and has started to come on when it wants even when the programmer is off and the room stat is turned right down,it fires up and the radiators come on,the only way to turn it off is to turn the thermostat/reset knob on the front of the boiler (right hand knob) to low,any advice would be appreciated just so when i get it looked at next week i have some idea what the fault might be,many thanks for your time.