My Glow Worm F55 boiler makes a kettling noise just before it switches itself off at the end of a cycle. No problem with the hot water or CH, just the annoying noise. Also my pump (Comet SMC 2-130) has three settings on it. I always have it on the first setting mainly because that is how it was when it was installed, but what do the other settings control. Ok, my boiler is 25 years old but is always serviced by BG annually and they always say it is in very good condition. Any suggestions please?