hi , i have limited info on this problem, the fan on the boiler seems to be hunting for power (1 second bursts) if the tube to the air pressure swith is removed the fan works correctly, when placed back into position the fan hunts for power again. the boiler has had a new air pressure switch, new fan, new fan drive pcb . sorry for the vague post as the symptoms were passed to me over the phone.
cheers
cheers