problem with baxi 100he plus boiler pcb?

had my plumber round today to replace pcb on boiler h
as he said other one had failed (no power to boiler mains is ok comming in been checked) anyway new pcb everthing ok for about 5 hours hot water central heating great! But then same fault occured no power on pcb board again plumber comming back tommorow but says he's never heard of that happening and does not really know what it is says he's going to phone baxi for suggestions but I have paid 200 pounds out today and my boiler still does not work is there anybody who might know what is the problem with boiler thanks jason