my potterton 80 boiler working fine on hot water, but heating is intermittent, i changed the external programmer as the old one sometimes stuck, the boiler would still not fire on heating demand, so i went to check the connection,s on the leads, and as i dropped down the front panel i heard an arcing sound then the boiler fired up could it be a bad connection on one of the wires or the pcb, any help would be grateful.