My boiler, a Glow-worm space saver F, has stopped working. Its normal
sequence of operation when starting up is that the flue extractor fan
starts running, then a spark electrode lights a pilot light which then
lights the main burner. However, now all that happens when you switch
it on is a clunk and a faint whirring sound (I'm not sure if this is
coming from the boiler itself or just water circulating from the water
pump). There doesn't seem to be any air blowing out from the flue and
there is no sparking at the pilot light. Does anyone here have any idea
what might have gone wrong and how to fix it?