I have a Potterton Kingfisher Open Vented gas central heating boiler with 7 radiators. The boiler developed classic "kettling" symptoms - lots of banging from the boiler that resonates around the system VERY loudly. I thought it was probably limescale baked on to the heat exchanger - a hard water area. I flushed out the system (dirty!) with Sentinel X400 cleanser and added Inhibitor and boiler noise reducer. Matters improved for about a week but now the "Kettling" has returned louder than ever - I am getting woken up before the birds - all suggestions welcome.