1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Discuss European / international water heaters, no expansion vessel in the Plumbing Forum area at UKPlumbersForums.co.uk.

  1. Jones82

    Jones82 GSR

    I've seen and heard about this a couple of times.

    When installing an un-vented water heater some parts of the world seem to fit an expansion valve and just allow it to blow off each time the water is heated.

    No expansion vessel is fitted on the incoming pipe work, they either fit it to a drain or just pop a bucket on the end and use it to water the garden.

    I've seen this myself, twice in Austria and I once worked with a lad from New Zealand who also said this is common practice.

    My most recent experience was on a 100l direct cylinder, fitted recently near Vienna. I managed to find the manual online and was surprised to see no expansion vessel is required.


    Scroll down for English :p

    Seems such a waste of water and heat and frankly I'm surprised the Austrians allow it.
  2. Stigster

    Stigster Plumber

    As far as I understand they aren't supposed to discharge every time they heat, the heated water is supposed to expand back up the main.

    Believe it or not we can even do that here but nobody does. You must calculate the amount of expansion required in litres and make certain that this amount of water can expand up the cold feed without reaching any other draw off point. It's in the regs somewhere, I'll go take a look as I can't remember exactly where I saw it.
    • Like Like x 1
    • Informative Informative x 1
  3. Ben-gee

    Ben-gee Plumber

    That’s how we do it for 10/15l unvented quite often - I suppose no physical reason why not on a larger cylinder provided long enough run of pipe to accommodate the expansion ( as long as no one tees off from this at a later date...)
  4. John.g

    John.g Active Member

  5. Stigster

    Stigster Plumber

    It's in the UK water regs, section 8.7. To summerise it says that the expansion vessel and check valve is omitted. It is essential that none of the expanded water can enter the supply pipe to be drawn off as drinking water. This would mean no teeing off the supply pipe within the distance the expanded water can reach.

    We just don't seem to do this, preferring to use an expansion vessel and a check valve to stop expansion up the main. The Europeans however seem to routinely use the expansion up the cold feed method.
  6. Ben-gee

    Ben-gee Plumber

    Has the advantage over an expansion vessel that it can’t go wrong and leak , so why not.
    • Agree Agree x 2
    • Like Like x 1
  7. Best

    Best Trusted Plumber

    That is true. The expansion vessels on unvented units are normally only made of light steel and seems to me to be a daft design. When the balloon membrane perishes - the steel eventually rots.
  8. Rob Foster

    Rob Foster Top Contributor!!

    Then the company that produces the rubbish makes more by selling the replacement, built in redundancy. Le Blanc produced combis with two circuits round the boiler, no diverter to go wrong that plus no exp. would be ace Rob Foster aka centralheatking
  9. chris watkins

    chris watkins Plumber

    The trouble is you need a lot of dedicated pipework for the expanded water before a cold tee. For a 15 Litre it is a minimum of 4.2 Metres. Often impractical if you have a small mains feed to a basin / sinks requiring both hot & cold water. (or at least it would cost a fortune in copper as you would have to run them separately).

    Just think of the pipe required for a 100Litre cylinder!
    • Like Like x 1
    • Informative Informative x 1
  10. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    9204759D-334E-4A37-B234-A80937A10314.jpeg How about this one , fuerteventura style lol
    • Like Like x 1
    • Winner Winner x 1
  11. snowhead

    snowhead Plumber

    2nd level safety is the flex hose splitting.
  12. Ben-gee

    Ben-gee Plumber

    I have just done back of envelope calculation and i think a 210 unvented cylinder would need 24m of 22mm pipe to accommodate expansion!

    This is 8 lengths - I’m thinking of fashioning some sort of clothes drying rack, now where did I put all those munsen rings?

    I think I might need to call rob about this invention too...
    • Funny Funny x 1
  13. Rob Foster

    Rob Foster Top Contributor!!

    Instead of using pipe you could pipe it up to a circular or rectangular water container located in the roof space ! hmmm it could be called an F & E tank, what an invention
    • Like Like x 1
    • Winner Winner x 1
  14. Jones82

    Jones82 GSR

    I see, thanks guys. Seems the theory is sound but rarely executed. The ones I've seen must not have had sufficient pipework as they were blowing off almost constantly
  15. chris watkins

    chris watkins Plumber

    Or the spring in the safety valve has worn through frequent use, it is now opening at a much lower pressure than that stated on the cap.
    This is a common problem in systems like this which is why, I believe it was the right choice to go down the route of accommodating expansion in vessels.
    Discharge is often not spotted by customers & leads to a lot of wasted mains water.
    • Like Like x 1