I suspect the shortages of the PCBs are linked to the chip shortages, given most modern boilers have reasonably complex electronic control systems.

As you say, you may find that the problem is just a dodgy contact, rather like with older washer-driers like my NEFF unit, where steam or moisture can get into the area where the PCB is and which turns the board/contacts slowly to black soot.

According to a very good YT video I've seen, with care, many problems (shorts, etc) can be sorted by cleaning the board/contacts with a clean, dry toothbrush, or using a quality electrical contact cleaner spray.

The problem often is that the PCBs have a LOT of contacts which aren't labelled and thus need to be catalogued/photographed when removing to know where to put back! Not so bad for a product costing £1k+ to replace that's 20 years old and well out of warranty that the local laundrette can replicate, not so good for a newer boiler with no heating alternative in case a self-fix makes it worse or dangerous.

My (then) brand new boiler had gas valve issues requiring the original and the replacement to be changed out in under two months - luckily both happened just before the pandemic kicked off, even if that was in the dead of winter and I had to wait 3 days (luckily I do have an emergency electic heater) for Vaillant to come out (nearly Christmas) the second time. Fortunately no problems (touch wood) since. I was glad that mine comes with a 10yr warranty though.

I hope yours gets fixed soon - not nice not having heat and hot water for extended periods.

E Bay may have one. I always try here for everything!

Seeing as a spammer brought this thread back to life, I may as well give a quick update. The new PCB was fitted together with a new flame sensor electrode and now all working again. Hot water and central heating - a treat, even if the weather's gone mild!