hi mate 300 quid is a bit steep for a pcb an fit try : googling "akgas.co.uk/Potterton-PCB/POTTERTON-SUPRIMA-PCB-KIT-5111603.html"
buy the part your self and get a gas safe installer to fit it shouldn't take more that a hourly rate and there's no make up on the parts. with the age of the boiler i would personally start to save up to replace it in near future
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