Mixergy Tank Failure

Domestic Hot Water & Cylinders

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bontwoody

(@bontwoody)

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Joined: 4 years ago

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Topic starter 13/09/2025 6:40 am

Hi.

I had my Mixergy tank fitted nearly three years ago and on the whole I've been very happy with it.

A week or two ago we noticed a small leak on the floor beneath the piping. Initially I thought it was a leakage compression joint which I nipped up.

This week I was woken by the sound of water and saw that the tank was discharging water via the tundish when heating. The most likely reason seemed to be a low charge in the expansion vessel, so I removed this and checked it. It was at 50psi.

I've contacted mixergy and they suggested I reduce this to 2.5 bar and monitor the situation.

It was at this point I noticed that the side of the tank seemed bulged out. When I had the tank installed the plumber pointed out to me a slight bulge in the outer case which I put down to over zealous insulating foam insertion at the time.

I recontacted Mixergy and they told me to stop using the tank and they would replace it under warranty. That was Wednesday and I have heard nothing since.

What I would like to know is what might have caused the problem and if it lies with the tank or the installation by the G3 plumber or the failure of a part, presumably either a valve or the expansion vessel which seems fine.

Images attached. Any comments welcome. Thanks

This topic was modified 2 hours ago by bontwoody

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JamesPa

(@jamespa)

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Posts: 2862

13/09/2025 8:56 am

OOh thats nasty. Unless your installer overpressurised it during installation, which is only really possible if you have very high pressure mains >>6bar, then its almost certainly a manufacturing fault, a fault with the heating element causing it to overpressure or a fault with the inlet PRV. Mixergy have clearly decided that one of these is the case as they have accepted responsibility.

Given the size of the bulge (50-100mm if I interpret the picture correctly?) Id be seriously considering living without running hot water for a few days, shutting off the supply to the cylinder and reducing the pressure to atmospheric by switching the taps on until they stop running. I'm surprised Mixergy didn't tell you to do that TBH.

Maybe I'm being over sensitive, but remember that this is a pressure vessel containing hot water, so bursting is not clever (hence the mandatory tundish arrangement). Clearly its failing.

This post was modified 16 minutes ago by JamesPa

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