Recently my potterton prima 50f boiler has decided to come on in the middle of the night even when the timer is stating it is off. As far as I am aware it is just the heating coming on,but the only way to turn it off when it does this is to unplug the boiler manually, neither the thermostat nor timer work(I suppose this is because they also think the boiler is off, or should be)!The boiler is turning itself on as the timer states it should be off or on timed. Then it will go back to working normally during the day then it will happen again the following night. I have been told it is more than likely the PCB! Is this correct.