Certainly what I was thinking.

It was quite iffy yesterday. It started fine but then, unusually, went off at some point not long after. So it was cold when we got up, and I wasn't popular. I reset it and it started then cut out again a few mins later. Normally once it's going it runs until it hits the boiler 'stat.

After that it was fine all day. Today it ran perfectly until about 11.30 when I noticed it was going chilly and found it was flashing red. It reset and ran fine.

What's different about these faults from the usual Suprima lock-out is it's going straight to flashing red - it's not doing the 3 tries at igniting (or re-igniting).

I do need to bite the bullet and try the other PCBs again, as at least one of them has to be exchanged back to Geoff.