Banshee noise from boiler

I've recently moved into a house with a 7 year old Halstead 55 wall mounted boiler supplying an ordinary tank fed hot water and central heating system.
After a while, when it all starts to heat up, the boiler begins to make a wailing type noise which can be heard all through the house. It stops as soon as the boiler stat kills the flame and if you set the stat lower it doesn't happen. The pump seems to be working fine and the problem's worse if it's just heating hot water rather than the rads as well. This implies it's related to either the boiler heat exchanger temperature or the temperature of the return flow.
Anyone got any ideas how to fix it or where to start fiddling, I want to turn up the boiler stat to get the rads hotter but at the moment I can't without the kids thinking the house is haunted.
TIA
Andy R
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It sounds like the boiler is kettling. This is usually because the heat transfer through the boiler exchanger is too low. This could be for a number of reasons. Some suggestions:
1. Pump knackered 2. Pump set too slow 3. Pump valves not open properly 4. Heat exchanger clogged/scaled 5. Most TRVs have turned off and bypass design/setting is insufficient 6. Pipe blockage/airlock
Christian.
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Andy R wrote:

When our combi did this, mostly on DHW, we found it was the pump itself squealing when the temp got to 82C. Turning the temp down stopped the squealing, but it seems to have cured itself now since we have been able to increase the temp again without the problem returning.
It sounded exactly like shot bearings, but possibly it was air since it went away by itself ;)
Lee
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To reply use lee.blaver and ntlworld.com


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sounds like when my powered flue fan went.
Steve

mounted
system.
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mounted
system.
Lime scale?
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You sure its a Banshee noise and not a hippopotamus? Only I know how to fix hippopotamus noises. Phil
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