Loud humming noise in micro bore central heating system

22 Oct 2006
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Newcastle upon Tyne
United Kingdom
I have a micro bore central heating system, fed by a Baxi 105e
combi boiler, which was fitted 2 years ago.
The heating system itself, radiators and pipework is approximatly 15 years of age.

I have a loud humming/whining noise from the central heating pipe work.
This has happened since the boiler was fitted, along with thermostatic valves to the radiators.
I did read that it could be the thermostatic valves, so I turned each one off in turn to see if it helped but with no difference to the noise.
Is this the right way to test, or do I need to remove the Thermostatic valves and shut the radiator valve off completly ?.

I also took some flooring up and noise appeared to be coming from the manifolds and pipework .
The noise starts as soon as the central heating comes on and continues even with the flame off but the pump still running.

I have read the info on this site, regarding central heating noise and in particular humming in pipework.
From this it would appear to be the pump, either the mountings, speed of the pump or too much water pressure in system.
The pump mountings appear to be o/k and the boiler is only 2 years old,
the central heating pressure is 1.5 bar, which I believe to be correct.
Can I adjust the pump speed on a Baxi 105e combi ?.

Could anybody tell me if there is anything else I should be looking at ?.
I would be grateful for anyones help/opinions with this problem, as it is driving me mad.

regards Feebee
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try turning the pump speed down. on the pump you will have 3 speeds
Do not alter the pump speeds on a combi. The highest speed is required for the HW function, and probably to avoid overheating in CH mode too.
maybe a system flush will help .. what is the condition of the water in the system does it smell when you open a air vent or black in colour ?
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Did they remove the antigravity valve (if one was fitted) when they installed the new boiler :?:
Thank you all for your replies.
I am not sure about the anti gravity valve, as I do not know what to look for.

When I bleed the radiators I do get some black water and it does smell a bit. Also the hall radiator has a cold spot at the bottom, which does not appear to be air, as I belive air would be at the top of the radiators.

If it is a system flush I need, could someone please advise me on how to go about it.
I have read that it may not be advisable to have a power flush on an old micro bore system, is this true.
If so what other type of flush is there.

regards Feebes

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