In message ernet.com,
Richard writes

Do you mean the pilot neon is flickering ?

Yes thats what i meant.
I probably didn't explain that very well the first time around.

The boiler on neon will also remain on if something is demanding
service.

Is the spark igniting the pilot but continuing to spark and not lighting
the main burner ?

The spark doesn't appear to be igniting anything at all.
Would i expect to see at least some gas usage from the mains supply when
this is occurring? (because i don't)

As I said, the pcb energises the PV solenoid at the same time as the
spark.

Are there volts to the pilot valve when it sparks ?

Yes ---------- faulty valve / solenoid
No------------ pcb fault

It might be worth checking that the PV solenoid isn't open circuit first

--
geoff