how to mend Gas Boiler, Glow-worm Fuel Saver 100F with SIT control?

Not an answer but I have much the same problem. I know it`s not the thermostat, I`ve recently replaced the pcb, but still get intermittent fault that the main flame does not light (pilot is no problem), but then comes on after half an hour or so. Could it be the gas valve?

pfm
March 2009

Sounds odd. If it's a fan flued boiler(and it sounds like it is) the thermostat must be functioning to bring the pilot gas on.
If it has an automatic ignitoin system, the pilot has to establish first and then stop sparking before the main flame solenoid gets power.
Unless iv'e mistaken the model the 100f has a small p.c.b to control the ignition phase. If it's the model i'm thinking of, if you turn the power off the pilot should shut down.

T.h.s
May 2007