the pilot has a restrictor in one end of the feed tube and a very swall hole in the pilot valve jet either is partley blocked which lets a small gas flow but not enough, once the boiler is fired up, as soon as its running the pilot goes out and turns the boiler back off this is a commom fault easy to fix. Be carefull when removing the pilot jet not to break the ignitor ceranic. also the restrictor on the other end of the pilot tube will fall out of the tube when you remove it from the gas valve. Dont increase the holes when unblocking as this will make the pilot flame to large. This has solved the problems on my boiler, and my nieghbours boiler. to avoid breaking the electrode remove it first by easing the little clip around the electrode and slidding it down and out of its fixing hole first before removing the pilot jet. DONT forget to make sure the gas and mains electric is turned off before doing any work on the boiler. am not a gas engineer but this is what I have found to solve the problem myself.
KTC, January 2009
