how to fix banging on turbo max plus vaillant boilerboiler?

boiler only bangs when heating is on and you turn the tap on for hot water it has already had the port valve replaced again this is third time is it possible that there a faulty batch ? si no 252457.three port valve E17 8143. the first time it was replaced the boiler was still under varrinty less than 9months old was told by vaillant own people that this was common fault as they used old type in new modle cant be that again can it .its less than 6months old new valve.

mr k vasey
March 2008