Megaflo must be totally vertical

Megaflo is a nightmare!

After six years of living with a Megaflo, which never worked properly, a few words from a guy who KNOWs solved it!

The ground the cylinder we installed it on was a little slopy, so we put in a little padding to make it level: or so we thought! :mad:

When you heat hot water using a boiler, the water expands, and the pressure was blowing the pressure valve at 6 bars, and the pressure made the face basin tap spew water at my lap. The internal diaphragm was supposed to absorb the pressure, and release it slowly when you use water. The original plumber tried regenerating the air gap multiple times, and even replaced the pressure valve on the cylinder, with zero success. And then he died! For years, I had to let the hot tap drip while heating hot water, to prevent the pressure build up.

Various plumbers subsequently suggested things like an external expansion vessel to take the pressure, and then never turned up to do the work.

Finally, an engineer turned up and says he has seen lots of Megaflo cylinder misbehaving, simply because the internal diaphragm tilts when the cylinder is not PEREFECTLY VERTICAL.
So we put in a few millimetres more of padding under two legs, regenerated the air gap, and it has been working how it is supposed to work for two days: BLISS!

It seems other manufacturers offer the same idea, it's just that Megaflo has the patent on the internal diaphragm, so other people have to sell you a system with an external pressure vessel, and they work EVEN IF the cylinder isn't level!

So, if you are going for a Megaflo cylinder, demand the Gas Safe engineer use a proper spirit level check all the way around the cylinder before plumbing it in. It's either that, or have a pressure vessel that looks like a big red zit.

I already have a big red zit, due to the under floor heating pipes having more water than normal radiators, so the built-in pressure vessel inside the boiler isn't enough.

I hope this helps to end the misery for Megaflo sufferers.
It was just millimetres!


  • Andy_WSM
    Andy_WSM Posts: 2,217
    First Anniversary First Post Uniform Washer Rampant Recycler
    Interesting. I have a premier 100L non-vented tank, which works lovely and is VERY well insulated (It's in a cupboard and you can feel no heat from it when you open the cupboard doors), BUT I also suffer the excess pressure problem you speak of. It does indeed have an external pressure vessel, charged to 3 bar as per spec. The solution for me was to heat it to 60C, not 70C which was the original setting. My plumber also suggested changing the pressure vessel to a larger one, but I find with the tank at 60C it's still more than enough for my needs - especially as the water to the bathroom is blended to 45C as it leaves the airing cupboard (with the full temperature water allowed to go to the kitchen where it's needed for stubborn dishes etc).
  • Cardew
    Cardew Posts: 29,034
    Name Dropper First Anniversary First Post Rampant Recycler
    Pincher wrote: »
    Various plumbers subsequently suggested things like an external expansion vessel to take the pressure, and then never turned up to do the work.

    Interesting post, thanks.

    Although a Megaflo does not need an external expansion vessel, I was informed it was mandatory in UK. This extract from the Megaflo website seems to confirm that view.

    7. What is the expansion vessel for?

    As water is heated its volume increases, and because water cannot be compressed, its pressure will increase. An expansion relief valve can relieve this pressure by automatically opening at a pre-set rating, thereby allowing water to escape and the pressure to reduce. However, UK water regulations/byelaws prohibit the regular wastage of water, so an expansion vessel is required to absorb this increase in volume. Note: Megaflo cylinders are designed with an internal air bubble, and do not generally need a separate expansion vessel. Either method allows the incompressible water to compress the air until an equalisation of pressure occurs. If water regularly drips through the tundish whilst the water is being heated, this may indicate faulty or undersized expansion volume

    Of course this might be a recently introduced regulation.
  • Pincher
    Pincher Posts: 6,552
    Combo Breaker First Post
    edited 29 October 2016 at 7:15PM
    Unlike water, air is very compressible, which is how Megaflo works.

    The idea is that the heating up process compresses the air, which pushes back when you run the taps, giving extra pressure, but it only lasts briefly.
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