Best course of action is,call Heat-Team[ number on baxi website], for a fixed price guaranteed repair.Alternatively arrange a call with British Gas to attend on a fixed price guaranteed repair of your boiler.On this boiler there have been quite a few modifications to the P.C.B.Re,moving fixed jumpers on the existing p.c.b.,alters the operation of the gas valve ,ignition and pressure to the burner.This type of work requiries a competant CORGI engineer.If you follow my advice,you will have a boiler with low start up ignition noise,smoother running, and you and your neighbours will be SAFE and happy.PLEASE LISTEN TO ME!Have the work carried out by a proffessionally competant engineer.Do not attempt any more hit and miss objectives,for your own safety.