Not to throw a spanner in the works but i regularly go on jv's with BG lads to these
BG lads 'we've fitted several harness, several boards' and yet the damn led3 lockout keeps coming back
Right have you checked the resistance of the plate ignitor? Anything more than 90 ohms boiler logic thinks its not lit and led will come on
So matey id just have a check of this before you fire a harness in.. Glow plug is a lot cheaper than a harness
Cheers, I think I'll stick a harness in anyway, (as I was getting intermittent strange readings from the flow sensor, and I've ordered it already!), but I'll also check the plate ignitor. I'm fairly sure that it's the harness though, (at least partiallly), as sometimes the boiler doesn't even get to the point of attempting to light before it aborts the startup process and the LED flashes.
I'll let you know how it pans out