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Unvented cylinder noise

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 Philip 26 Aug 2014
I've just had an unvented HW cylinder installed as part of a new heating system. I had asked for a whole house pressure reduction valve as the mains pressure is high - enough that the previous owner had tried to temper it using the isolation valves.

The cylinder itself has reliance multibloc 6bar, which I think is 3bar reduction and 6 bar pressure relief all in one. The white expansion vessel is factory set at 3 bar and I'm not sure if that was checked by the installer or altered.

When any hot water outlet is partially opened there is a continuous fog-horn noise and associated vibration. This goes when the outlet is fully opened ans returns as it is closed (stopping once closed). It's not trapped air and it's not air-hammer.

I've contacted the plumber, via the renewable installers, but as the noise could be one of several things I wanted to see which of them needs addressing - as some of them I will have to pay for.

1. I can have a whole house pressure reduction valve set at 3 bar.
2. The expansion vessel - should that be set at the reduction pressure or the relief pressure. I know it's a G3 issue, I'm not tackling it myself. I suspect the 3 bar reduction isn't achieving that and the noise is from the expansion vessel.
3. The incoming water main is plastic, at least 22mm. It is reduced to 15mm before the stopcock and stays at 15mm until just before the pressure reduction valve where it change to 22mm. It's not a massive job to replace this with 22mm all the way (quite accessible) - would this help.

My thinking with 3 is that the increase back to 22mm is causing the turbulence that is making the valve noisy.

 jkarran 26 Aug 2014
In reply to Philip:

Sounds to me like the hum could be the pressure reduction valve not working well under light flow conditions causing the pressure & flow to fluctuate rapidly, chances are once your tap is wide open the regulator is seeing <3bar at the outlet and is wide open and not therefore resonating.

It's also possible the valve performance is normal but somewhere in your system there's a pipe-run or bend that vibrates noisily under fluctuating flow conditions. Fillers on cisterns are the usual culprit for driving this type of banging/humming noise as the flow varies with the ripples on the cistern surface before closing off completely.

There are plenty of ugly joints in the average plumbing system, I'd be surprised if the step from 22-15 or back is driving your resonance.

Surely whoever installed it should be willing and able put it right, it must be a common enough problem and I presume you weren't quoted for musical pipes!

jk
Post edited at 16:20
OP Philip 26 Aug 2014
In reply to jkarran:

They will put it right as there's 25% of a £21k bill still to be settled once I'm happy with the system. All singing and dancing is what I wanted, but not musical!

I'm going to try and borrow a pressure gauge from one of our maintenance guys tomorrow and measure the pressure of the incoming mains and the hot water after reduction.

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