Recent sudden increase in boiler noise

11 Dec 2007
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United Kingdom
I have a 9 year old Worcester Bosch 28SiII Combi boiler which has worked quietly and well so far. At the end of August, I had a radiator replaced and the boiler serviced a couple of days later. The heating hasn't really been used until October.

Two symptoms have seemed to start at pretty much the same time:

1) The boiler is suddenly rather noisy for 5-10 minutes after the CH first comes on, making loud kettling noises (but no banging). After 10 minutes, it runs quietly as normal. I'm guessing some scale/sludge has partially blocked the heat exchanger.

2) (a) When turning on any hot water tap with the CH fully off, there is a noise sounding like roaring air (like an aeroplane flying overhead, but not a mechanical noise) which lasts for about 4 or 5 seconds. The noise starts very soon after the boiler fires up on demand to heat the water. No noise when the tap is turned off.
(b) If the CH is on but not actually heating radiators at that precise moment (no red light on front of boiler), same as (a) when turning on any hot tap.
(c) If the CH is on and actually heating radiators at that moment (red light is lit up) then the timing of the noise is reversed. In this case, the roaring air noise happens for 4 or 5 seconds after the hot water tap is turned *off*, not when it is turned on.

Both the kettling and roaring noises are loud enough to be heard all over the house. The roaring sounds a little like the kettling, but more violent.

Any ideas? Could these symptoms be related?

Thanks for any advice,
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I have edited my post above to be more specific regarding the timings and nature of the noises. Any suggestions most welcome - it's always good to have some idea of the fault before calling someone out.


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