Noisy central heating in bypass

22 Dec 2005
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United Kingdom
In our new house we seem to get quite a bit of flow noise when the both the motorised valves are closed and the bypass valve is working.

We have a Glowworm Ultracom 24HXI boiler supplying around 14 radiators (all with TRV's apart from the hall radiator and the bathroom towel rail) and a Megaflo.

There are two motorised valves, one appearing to control flow to the megaflo and the other controls the flow to radiators.

When the water in the cylinder gets up to temperature one of the motorised valve closes and if the central heating is not on all water flow seems to be through the bypass which is emanating quite a bit of flow noise.

Same thing happens when the thermostat in the hall clicks if the hot water is not on or it is on but the cylinder is up to temperature.

Under either of these conditions the boiler stops firing, the motorised valves close but the pump runs on (presumably to stop the boiler from kettling) which means all the flow is through the bypass which is then very noisy.

Adjusting the bypass valve makes no difference to the noise (yes i did mark its position and return it back to where it was after fiddling).

Does it sound like the system has been plumbed correctly and can i do anything to reduce the noise from the bypass valve?

Thanks in advance
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Is it the bypass an automatic type or a manual gate valve, and what size pipe is the bypass piped up in, ie 15mm or 22mm?
It does appear to be piped up correctly from your description of the system.
The bypass looks to be a propriety type valve and is certainly not a standard gate valve. I haven't seen a bypass valve before to compare it to but it has a black plastic adjuster knob on it with a screw to lock it in place.

Its not 15mm. I think its 22mm but some of the heating pipework in that area is 28mm so it may even be that.

Manually overriding the motorised valves quietens the system down instantly and when those valves are open i can't hear any flow noise from the bypass valve at all.
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Photo of bypass below. Its definitely a plumbed in 22mm:


Can anyone offer any advice? Is noise typical from these valves or is mine faulty?
Its normal for those valves to be somewhat noisy.

It only lasts as long as the boiler pump over run which is for a few minutes.

Because they are normally in a cupboard its rarely a bother.

Are you someone who lives in a quiet house with no radio or TV on and listens to every slightest noise?

I assume that the pump over run does eventually stop as it should.
The only thing I can suggest is to remove and clean or replace the bypass valve. It does look like 22mm. Follow the guide in setting up the valve.
Bypass valve is located in the airing cupboard which has a common wall with our 11 month old son's bedroom. He's proving to be a very light sleeper, there is a fair bit of noise coming from the bypass valve so its waking him up every time the bypass is operating.

It is only noisy on the overrun, and the pump does indeed stop after a couple of minutes. However, this does seem more much noisier than i would expect.

I want to find a way of reducing the noise, hence my post. If the noise is just what you get with this sort of system, i need to then look at insulation to reduce the noise transmitted through the wall into his room.

We are not the sort of people who sit in a silent house with everything turned off listening specifically for a noise to complain about :). This noise does seem abnormally loud.
It would not normally be more than 48 dB A @ 1m.

You could try wrapping it with blanket like material.

But before you do that feel it when its operating to see if the pipes are vibrating.

If so see if you can feel a vibration node that when touched lowers the noise level

I wouldn't know what 48db at 1m sounds like, but could borrow our sound meter from work and find out it is producing :)

The noise is definitely flow noise rather than vibration. The pipes are quite well clipped to the wall, with the exception of the branch that contains the bypass. I'll try clipping that to the wall first and if that doesn't work i'll try wrapping the valve in a thick layer of rocksill.

Is there a problem with me insulating the bypass branch pipework around the bypass valve? Does it need to be exposed to enable it to radiate some heat to prevent kettling?

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