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Expansion vessels on hot water cylinder. Are they designed to fail?

Discussion in 'Plumbing and Central Heating' started by Rad1o, 12 Jul 2019.

  1. Rad1o

    Rad1o

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    We have had a copper hot water cylinder with an expansion vessel fitted around 2003. We had a leak on the second expansion vessel in this time. While the first one just vented water from the air inlet valve at the top and was not too much of a problem until I got a new one, this "new" one had caused a major and sudden leak where water has bypassed the flange and caused the vessel to rust and leak.

    Are there any expansion vessels that will not cause a leak?

    Don't get me wrong, I love changing them, but the manufacturers wright in the instructions that there are no perishable and serviceable parts on the vessel.
    Now I have got one from screwfix which is certified to a higher pressure than the last ones.

    The vessel is charged to 3bar and we have a pressure reducing valve and blow off valve fitted.
     
  2. Gasguru

    Gasguru

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    Lack of annual servicing and topping up of the vessel air pressure causes most problems.
     
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  3. bazdaman

    bazdaman

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    What colour was then replacement vessel?
     
  4. ianmcd

    ianmcd

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    when it says that the expansion vessel should be serviced every year , have a guess what that means
     
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  5. ollski

    ollski

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    A 3 bar vessel is for unvented hot water not central heating and will be unsuitable to replace a 0.7 - 1 bar ch vessel, you know that right?. Just checking.
     
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  6. muggles

    muggles

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    Refix vessels carry a 5 year warranty. They do need servicing annually though
     
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  7. bernardgreen

    bernardgreen

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    How do you "service" a domestic expansion vessel ? Can you open the vessel to inspect the membrane or diaphram for excessive wear and tear that would require the vessel to be replaced ?.
     
  8. Rad1o

    Rad1o

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    Thanks for the comments.
    The old vessel was a Varem and the new one is a Refix. The Varem was certified to 8bar, while the Refix is certified to 10bar. They are charged to 3bar.

    One of our neighbours, who is a plumber for water and gas who modified our CH system to a pressurized one but did not fit the hot water system did an annual service.

    The annual service of these vessels and the system around the hot water cylinder is not very high tech.
    It consists of a visual check, pressure check of the expansion vessel and recharge if necessary, a check and test of the temperature and pressure blow off valves.

    Correct me if I am wrong on the items listed.

    I opened up the old one at the flange expecting a puncture in the rubber membrane. It seemed completly intact but there was a lot of muck between the steel skin and the rubber.
     
  9. Madrab

    Madrab

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    You are correct as far as the list is concerned, there are another couple of checks re strainer/filter, thermostat and operation of 2 port valve if fitted.

    If this attached to an un-vented hot water cylinder though then it isn't really a DIY job, and unvented cylinder should be serviced/repaired by a qualified engineer.
     
  10. muggles

    muggles

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    Depends on the manufacturer, but yes some can be disassembled for inspection. Keeping it at the correct inflation pressure helps a lot with longevity though
     
  11. Rad1o

    Rad1o

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    The leaking Varem could only be disassembled with a hacksaw.
     
  12. DP

    DP

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    There are two types of vessels. One is made for boiler systems and other for hot water systems. Fitting a vessel designed for heating systems onto a hot water cylinder is a no no as it will contaminate the expansion water
     
  13. bernardgreen

    bernardgreen

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    What will be the material than contaminates the water ? Chemical(s) leaching out from the membrane perhaps ?

    Which suggests that the membrane in a vessel designed for heating systems will over time degrade and fail.

    Assuming both types of domestic vessel use a diaphram and neither uses a balloon. If the membrane in a vessel for hot water systems does not contaminate the water then the membrane in that vessel ( in theory ) will not be leaching and degrading. Why not use the same material for both types of vessel ?. Is it the cost of the better quality membrane ?
     
  14. dilalio

    dilalio

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    It's not really the membrane. It's the metal casing used for the application. Wholesome water from a mains supply (with all its added minerals and chemicals) will eventually corrode an EV that is designed for CH, leading to catastrophic failure and lots of damage (seen it first hand).

    DHW EV's are built from materials that can withstand mains water.
     
  15. bernardgreen

    bernardgreen

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    Thanks for the explanation.
     
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