It is not a ****e thing, it is an easy fix on a solid boiler and the last fault was not a dusty air pressure switch as they're sealed. If the guy changed it last time because he told you it was that use someone else this time. PCB is expensive but that can happen to anyone, the recuperator is very expensive so get it serviced properly and get him to include cleaning the recuperator which will save you a packet.
Great response - many thanks