baxi bermuda inset2 boiler 50/4?

boiler had been shut down for about 3 weeks i put the controls to constant the boiler green light came on the boiler fired then went off no lockout came on this happened for about 5minutes it then fired up stayed on for about 5 hours went to bed put it on timer it did not come on in the morning i switched it off then after s short time it tried to fried up again the same sequence as before but this time it failed to start called a boiler repair man who changed the pcb but that did not make anydifference then changed the potentiometer that also did not make any difference we are still without any heat or hot water awaiting the return of the boiler man any help out there we are both oap and cold.