I hope this helps in some way, I had the same probs with mine, i replaced the diverter valve, cleaning the 2 feed pipes aswell as a little calcium had built up in the ends, 2 thermisters/2 flow switches/auto air vent/pcb and igniition leads, and still it did not work, only 1 thing left THE AIR PRESSURE SWITCH which someone mentioned some where on this site, THANKS, ITS NOW WORKING A TREAT, its now like a new boiler with all the new bits added, and it should last a few years more now,
daren
October 2009