please help with my vokera boiler?

Hi can anyone help me with my boiler problem my boiler is a vokera compact 24 been having problems for about a year now boiler fires up ok but sometimes only runs for ten min if not less than that and red light comes on i need to turn off and on again sometimes it works but not all the time it also does this when running the hot water I sometimes once reset run kitchen tap first wait till if fires then run bath tap and it works is this normal.i also notice that when I turn thermostat down on boiler it goes to red. Recently I have heard a banging noise from boiler once it has locked out when boiler runs I hear a clicking noise from my first radiator is this just the radiator heating up
I have had the expansion vessel PCB board overheat starter and main sensor replaced but none of these have worked the last engineer I had out to look noticed the flue on boiler was the wrong one could this have anything to do with it please help thanx

jim
December 2011