HELP WITH MYSON HOUSEWARMER?

Need some help with a Myson Housewarmer 55 electronic. No ignition. No manual. I am corgi registered and went to look at this boiler. checked all the obvious and came to the conclusion, possible PCB, but wondered if anyone with a greater knowledge on this type of BBU could throw some light on the subject. The PCB is the one mounted on the side of the back boiler not the later red type at the front. Listed as Thorn PCB. There is no sparking at the electrode, but if you remove the multiplug off the top of the PCB it then starts sparking, but does not open the gas valve. I suspect because the plug is disconnected ? Any ideas, I dont want to just jump at a PCB as it is a special order and PCB's are not returnable. Thanks for any help.