I'm an engineer, although in electrical appliances & steel design rather than gas installations.
Read through any similar forum on here & you'll find many helpful suggestions not disregarding your above caveat.
So the PCB, has anyone resolved similar by changing the board ?
I've been through quite a few of these forums hoping to track down my fault with varying levels of success.
About 3 months ago the boiler started acting up, flame would could out early in the cycle with a flue fault being indicated.
First thing I changed was the APS, at the same time I checked...