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Mixergy Tank Failure

bontwoody · 2025-09-13T05:40:14Z

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

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Domestic Hot Water & Cylinders

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Mixergy

(@mixergy)

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16/09/2025 9:27 am

Thank you for raising your concerns. Customer safety, service and appliance quality are our highest priorities. We’re sorry for the worry this has caused.

Our team is already working to get this resolved under warranty. We’ve advised you to stop using the cylinder and we’re coordinating with our service partner to arrange a replacement. We’ll follow up directly to confirm the appointment details.

For privacy we won’t discuss diagnostics publicly, but we’ll complete a full assessment and share our findings with you.

In the meantime, please keep the unit isolated (power/heat inputs off). Thanks for your patience, and for flagging this with us.

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bontwoody

(@bontwoody)

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Topic starter 16/09/2025 3:22 pm

@mixergy Thanks for the update, I would appreciate some kind of timescale as soon as you are able to give one as we are totally dependent on this for DHW.

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bontwoody

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Topic starter 27/09/2025 9:23 am

Just an update on this. I had an email from the technical dept shortly after the Mixergy post above, confirming everything was in hand and they were organising delivery of a replacement cylinder and would then book an installer.

However since then no word, so it will be 3 weeks next Wednesday. Ive managed to jury rig an electric shower so we at least have washing facilities, but if I wasnt able to do that it would be a nightmare.

Going to try and get some word off them next week.

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Toodles

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27/09/2025 10:17 am

@bontwoody 😟 You are a lot more patient (or charitable towards such companies!) than I would be. I don’t feel your experience has been a very good PR exercise for Mixergy. Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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bontwoody

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Topic starter 27/09/2025 4:47 pm

@toodles Im trying my best but it is getting a tad tedious

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bontwoody

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Topic starter 03/10/2025 3:40 pm

So after waiting over 3 weeks for a replacement cylinder, it arrived yesterday and the installer arrived this morning. Unfortunately he didnt know what the job was prior to getting here and didnt have the required fittings so will have to come back (3 hour drive from Brecon).

He was puzzled by the fact that the cylinder ports didnt seem to match the schematic and I agreed to try and contact Mixergy about it. I didnt get an answer this pm, but I did look at the cylinder they have supplied and as well as not being the slimline version that I had previously, it also turns out that it is an indirect tank not a direct one as I had.

It should just about fit in the cupboard but im not sure about the consequences of it having a coil. Will it reduce the volume of water heated, should the outlets be capped? Or should I just try and get Mixergy to send the correct cylinder regardless of the wait!

I am getting a bit frustrated with them!

This post was modified 5 months ago 4 times by bontwoody

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Old_Scientist

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03/10/2025 4:09 pm

All else being equal, having an indirect heating coil will reduce the volume of water the vessel can hold. But as you are not comparing like for like (it's a cylinder of different dimensions), I guess the relevant question is how does the internal volume of water compare to the cylinder being replaced, and is the difference an issue to you? I don't see that the coil needs capping off if not in use, but presumably it does provide a potential source of additional heat loss as hot water will heat the air in the coil which can exit and be replaced with cooler air, so from that perspective I'd cap the coil to help prevent heat loss.

I wonder how stratification efficiency will compare on a slimline vs regular tank?

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bontwoody

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Topic starter 03/10/2025 4:20 pm

@old_scientist Well they are both nominally 120L so maybe it wont matter. I was worried if the expansion of air in the capped coil would be a problem but its hard to imagine the pressure would exceed the water pressure in the tank.

Regarding the stratification efficiency, its an interesting question. In a narrower tank there is less area of contact between the hot and cold water so my bet would be on the narrow cylinder being better.

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Old_Scientist

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03/10/2025 5:24 pm

Posted by: @bontwoody

↑

Regarding the stratification efficiency, its an interesting question. In a narrower tank there is less area of contact between the hot and cold water so my bet would be on the narrow cylinder being better.

My thinking exactly, but I don't know whether it would be significant enough to be concerned over.

Given how long you've waited for a replacement, I doubt you're minded to reject it for a like-for-like slimline replacement.

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bontwoody

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Topic starter 03/10/2025 6:01 pm

@old_scientist that was my feeling so long as the unused coil didn't prove to be an issue 😁

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Mars

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03/10/2025 8:08 pm

Posted by: @bontwoody

↑

So after waiting over 3 weeks for a replacement cylinder, it arrived yesterday and the installer arrived this morning. Unfortunately he didnt know what the job was prior to getting here and didnt have the required fittings so will have to come back (3 hour drive from Brecon).

The amount of times this happens is staggering. Driving across the country to do a job and not fully briefed or prepared. Was this an installer from Mixergy or someone that was assigned to you? Truly staggering.

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bontwoody

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Topic starter 03/10/2025 8:16 pm

@editor someone Mixergy assigned Mars.

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