Kyote, in the nicest possible way, can I point out that it would have been far cheaper for your mate to call in an RGI to look at his boiler than to get you to replace the pcb.
I know it is easy to be wise after the event and I don't mean to sound smug. Make sure the professional your mate calls out is experienced in boiler repairs - not just a parts swapper.
Be nice if you could post back and let us know the outcome. Good luck buddy!
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