On my Profile Boiler there's a fuse on the PCB control board. You sound like a heating engineer guessing before diagnosing. The sequence is - Call for heat - Fan runs - pressure switch makes - pilot gas valve opened and spark ignition. Good luck with the fuse - it's smaller than a plug fuse - 20mm long rated 1A and 250V - Just to the left of the big connector - loose wires close by - Earth Brown Blue & 2 White