NRV noise.

24 May 2008
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United Kingdom
I had a Megaflow unvented cylinder fitted about 3 years ago. I have a problem regarding the non return valve in this system in that whenever hot or cold water is drawn off, the nrv slams shut with a loud thump like a hammer blow on the pipework. I have tried reducing the cold inlet feed pressure (with a prv) and reducing the draw off flow pressure (again using a prv) to no avail.
I previously had a similar unvented cylinder by Albion which, although using a prv on the cold feed, was silent in use for 15 years.
Advice would be appreciated please, thank you.
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Is it a new problem or since install.

Has any work been done prior to the problem.
Reducing the inlet pressure will have no effect on your problem. It is the reverse pressure that's causing the water hammer. You'd probably be better increasing the setting on the PRV.

Alternatively, you could fit a hammer arrestor.
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Thank you for your replies.

My initial posting referring to an Albion cylinder should read an nrv, not a prv.

The fault has existed from day 1. The installation company fobbed me off and arranged for a chap from Heatrae Sadia to inspect the cylinder. In spite of sitting by the cylinder while I demonstrated the noise, he said he did not know the cause. It would seem that I have not been assertive enough!

I am willing to fit an anti-hammer device and would appreciate advice regarding where to install same. Should it be sited as close as possible to the nrv and do I need one for each of the hot and cold draw offs?

Thank you.

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