Noisy central heating

[DrUdgery]

Hi - newbie here hoping someone can help with advice.

We have a Worcester Bosch Greenstar condensing boiler with an unvented Ariston cylinder. Sometimes there is a loud vibrating/rumbling noise from the central system. It is intermittent but seems to be when the boiler is running at full power to heat the rads as opposed to just hot water.

The noise doesn't seem to emanate from the boiler itself, at least, it is not significantly louder at the boiler than downstairs where you can hear the noise reverberating through the pipes.

A minute adjustment of the nut on the valve(?) below the boiler in this picture (if I can make uploading work) will usually stop it temporarily, but it will return.

Can anyone give any advice and also tell me what this nut/valve is and whether it should be fully open/closed or not messed with at all on pain of death?

I do have a service contract and the boiler was serviced at the beginning of the year, but if the problem is in the system the contract won't cover this, and inevitably, with my luck, I doubt it will make the noise when an engineer is here to look...

Thanks to anyone having a read

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• DrUdgery
• 13 Dec 2014
• 1

 

[Gasguru]

The "nut" is an auto bypass valve and it will have been adjusted when the boiler was installed.

Have you got thermostatic valves on the system? It's possible they are generating the noise. As a starting point you could fully open them to see if that's the source.

 

[DrUdgery]

Thanks Gasguru

I take it from your reply that the auto bypass valve shouldn't be touched then? How sensitive are they? This morning the noise stopped when I turned it by the tiniest amount - you couldn't tell the spanner had moved. Would that be enough to affect the original adjustment in any significant way?

Thank you for the TRV tip - I will try those now.