In message , Cod Roe
writes
geoff wrote:

Assuming that you are getting a spark and GV operating, i.e. that
there is a flame to sense ...

Yes, there is a flame to sense.

1) pcb - unlikely from what you have said above

I'm not paying for another one to test that further!

I can test Eco 80 pcbs

it's what I do


2) break in the wire from the electrode to the pcb (are you really
getting 5uA ?) the only way I know of reliably testing the lead is to
give it a tug at both ends to see if the wire is attached to the connector

I have checked the resistance from tip to spade with a multimeter and
all is fine.

You didn't read what I typed, did you ?


3) Electrode not in the flame

The thing is rigidly fixed, though slightly off the flame, and the
boiler just failed in service without anyone having been near it for
months, so I doubt it had moved. Anyway, I measure a current once it
lights.

Whatever, if the electrode is not in the flame, it won't flame sense


4) bad earthing

The earthing hasn't changed, but could you elaborate? Water and gas
primary bonded to the boards riser, and the ring main earth is fully
functional.

flame sensing is referenced to earth

if there is a problem with the earthing anywhere within the boiler, this
could cause problems with flame sensing (including to the pcb)


5) Live and neutral transposed (unlikely unless you have recently
done some electrics)

Had that some months back, when the plumber had kindly put both ends
the wrong way round, how anyone can do blue to brown and brown to blue
without feeling guilty I don't know.

So you have let a clueless dickhead near your boiler - best check out
the wiring again then, just to make sure


I checked the gas valve with a manometer and it seems to be delivering
full pressure.

and ?

like measuring the temp sensor - a red herring



About to give up on this one, and maybe get a Worcester Bosch Greenstar
30Si to replace it, anyone got any comments or suggestions for a better
machine?

I have listed the possible reasons for a lack of flame sensing, go and
work through them properly. Start at the beginning, don't make
assumptions and don't take anything for granted - it's easy to overlook
something that you think must be OK

If you want the pcb checked out, I can do it

www.cetltd.com

but I think your problem lies elsewhere

--
geoff