Ariston EuroCombi Flame Detection?

Relating to another posting

http://www.howtomendit.com/answers.php?id=38227

I have a 23MFFI, and intermittantly the boiler tries to relight itself (even though it is burning fine) as though it thinks it has gone out and sometimes (if it thinks this for 7 seconds) it locks down and needs resetting. The boiler always fires up first time.

I have had the detection electrode replaced, but has made no difference.

Would this be a similar thing to the attached link (i.e. need a PCB change or could be due to something else (e.g. dodgy earth?), due to its intermittant nature.

If so, which PCB would it be?, as the flame detection circuit is on the power PCB, but the logic for the shutdowns must be on the Electronics PCB. I don't want to have to get both of them changed if possible.