A long time ago and on a previous hot water cylinder we had a wetback and therefore an open vented stand pipe acting as the pressure release.

The piping was in the way and would track in water during rain so I had a plumber replace it with a Methven NEFA NRV76 pressure and vacuum relief valve.

However, it makes an inordinate amount of noise (as you can hear here) and dumps water with each use of the taps or showers connected to that cylinder.

We have a gravity fed system running off header tanks. There are a mix of separate hot and cold taps, mixer taps with and without aerators, showers with separate taps and mixer handles. All permutations lead to the same behaviour.

We haven't been able to get the plumber back yet to see if they can resolve it. My discussion with the Methven support agent is below, but wondering if there's any additional expertise in the forum that might lead to other avenues to explore.

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(Me)
Thanks, the same effect happens on non-mixer single supply hot taps as well as mixers on full hot without aerators. The hot water cylinder and cold taps are fed from the same gravity fed header tank location so pressure should be equivalent. We have three other hot water cylinders that don't have the issue (but with different pressure relief valves). I'll explore non-return and restrictor options. In the case of the issue occurring with taps that are purely hot feeds, would a pressure reducing valve and/or cold water expansion valve on the HWC inlet address this? Or should a 12.2m valve on the overflow be investigated before reducing inlet pressure?

(Support)
Re your email se below

His issue is cross feeding - most likely with the sink mixer. Possibly still got a flow restricted aerator fitted (or has developed a blocked aerator) and the high pressure cold is blasting back through the hot pipe to the cylinder, where the relief is doing what is designed to do and relieving excess pressure.

To resolve it

Unblock aerators
Remove any flow restrictors post mixing
Put flow restrictors or non returns on the cold inlets

and the problem should go away.

Hope this helps

(Me)
Hi there, the noise from our NEFA NRV 76 valve has become persistent with every use of the taps over the past few months with an associated spurt of water each time, and sometimes sings quietly to itself for a while until it reaches equilibrium again. It's very aggravating, especially at night. Attached is an audio sample of the tone. The plumber hasn't made it back yet. Would it be likely that we need a unit rated for 12.2m of head? I would imagine our header tank isn't that high above the HWC inlet but it could be between the two.

(Me)
Thanks for your reply, would it be possible to ask for further clarification?

Yes, the wetback is no longer installed.

We have a gravity fed system from a header tank for all our water but checking this morning, the behaviour is as described (a little gush of water accompanies the noise when relieving pressure, it has filled a 10l bucket since Wednesday morning). However, we haven't noticed regular over-flow from the vent pipe previously, it is very tall and may have had enough height beyond the header to accommodate normal expansion (back in the days of the wetback it used to vent when running very hot).

The noise and gush also is associated with use of a couple of non-mixer single source taps though. I've attached a diagram, the non-mixer taps are on the bath and in the laundry.

Would you advise non-return valves for the cold supply on all taps and showers?

Thanks for your assistance.

(Support)

Good Morning

Thank you for your enquiry re Nefa Valve problems This is the reply from the tech guys

and this is his reply

I assume there is no longer a wetback installed. Wetbacks (uncontrolled heat source) must be open vented.

As for the woodwind section tooting a tune...

if they have mains pressure to the sink mixer, it is possible they are experiencing back pressure from the cold water. This may be over-pressurising the cylinder as it back feeds down the hot line, in which case the valve is doing exactly what is should - relieving excess pressure. This will be evident by a gush of water out of the drain pipe, particularly when using the sink mixer. it would have been happening before, just the gush would be out on to the roof. Resolution - install a non-return valve on the cold supply to the sink mixer.

If it is just thermal expansion...no it shouldn't be whistling Dixie.

depending on hot water usage, they might expect between 2-4 litres per day of thermal expansion. This is not wasted water per say, just the change in volume when water is heated.

Hope this helps

(Me)
Subject: Nefa relief valve noise in normal operation?

Hello, we've just had an NRV 76 relief valve installed on our gravity fed hot water cylinder to replace the open vent left over from when we used to have a wetback system. We've noticed that after every use of the tap, there will be a little clarinet call from the valve/tubing which I'm assuming is associated with re-equalizing the pressure but just wanted to check if that is expected behaviour or if we should be bleeding air somewhere? Or using the setting instructions to expel water through the valve and then reset the adjusting screw?

Thank you for your assistance.