Thermostat has intermitant fault ie it stays open circuit and does not allow boiler to re-light. Main gas valve runs on Pilotgas but main gas solenoid is sticking and takes 10/20 minutes to open.
Gas valve is still available Part No 800125 but Thermostat Part No 202516 is obsolete.
Does anyone know of replacement parts or how to service the faulty items.
Or I would like to replace Boiler with same or similar.
Yours Hopefully Kev Mac

Kevin McLeish, May 2007

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