I have a Glow-worm Mark2 (oldish) boiler and the pilot light works, but when it fires up, it (and the pipes) make a loud banging sound, the radiators upstairs get hot, then go cold again very quickly...We've bled all pipes/rads but to no avail :( Anyone know what they think this may be please?? Thanks!

Kappachino, November 2013

Make sure header tank is full of water ,and ball valve is in working condition ,lot of air is system ,look like it's running dry ,place boiler low temp ,connect hose pipe to drain out valve or you may drain out already out side property ,open valve let water out small amount at time ,if head tank is fill up than they is no blockage ,if no, than it's problem ,need engineer to clear

ltd, November 2013