I have a worcester 28cdi Combi boiler that is constantly switched on allowing me instant hot water at the turn of a tap!! recently we woke early hours as the heating was on and have found out now that we cant turn it off unless we unplug it...
This now means every time we switch the boiler on so we can get some hot water the heating automatically comes on also... I have tried the reset button but it doesnt seem to reset it at all!!! HELP.....
Could be that the Mode Switch on the Control PCB is faulty. I have had this problem too and the central heating works at full tilt until you turn the electric supply off. Whilst I cured this with a little switch cleaner I would not recommend this kind of work to anyone not qualified.
You should contact Worcester - looks like it requires a replacement PCB.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.