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Cold water backfeeding - Unvented cylinder

Discussion in 'Plumbing and Central Heating' started by Marconar, 17 Apr 2021.

  1. Marconar

    Marconar

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    Hi there

    I recently had a problem with backfeeding of cold water in the hot water tubes, I have an unvented direct cylinder. We tried all mixers but apparently the issue was caused by the valve visible on the pic attached. We closed the valve and all seems to be working. The plumber is not sure what that valve is and my neighbors don't know either.. what could it be? Thanks
     

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  3. dilalio

    dilalio

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    Where is the expansion vessel?
     
  4. ChrisR

    ChrisR

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    I don't see how we can tell if you don't say what it's connected to! I suspect it's just the hot feed and you had flow from the EV -leave it open. SInce it doesn't have hot and cold going to it, it can't be responsible for mixing.

    Draw your circuit out, for your own education really, including the EV. The fault WILL be a mixer tap - they can go porous etc.
     
  5. bernardgreen

    bernardgreen

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    Does the plumber has G3 certification ? Plumbers who do work on unvented cylinders should be G3 registered as proof of their competence to work on pressurised systems
     
  6. DP

    DP

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    Good chance the cold feed is at mains pressure
     
  7. Marconar

    Marconar

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    I don't think it is connected to something, the valve now is closed and all is functioning well, the hot water is flowing normally. A theory is that it could be some sort of pressure reducing system but there is no visible pump connected to it. The expansion vessel is on the left and the pressure is ok in it. Plumber was from pimlico plumbers, actually 2 different plumbers attended, not sure they have g3 or not. Initially they thought immersion heaters failed because they were dead but then realised probably they failed ?because of the back feeding. Now the tundish is dropping very slowly but dropping a little and I will consider changing the whole system but before doing so I would like to be sure of what that is and that there is not a residual back feeding.
     
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  9. dilalio

    dilalio

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    If the left branch of the T, below the inlet group, goes off to the EV, then the other two branches (going right) will be balanced cold feeds, before cold into cylinder. That valve may supply another mixer valve somewhere... Need to trace it to be sure.
     
  10. Marconar

    Marconar

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    Have a look if the new pic is more clear.. left side there is just the expansion vessel. I wish I could avoid tracing it, I am asking if neighbors can find out a plumbing system diagram :( thanks guys you are amazing, i like this forum
     

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  11. Nige F

    Nige F

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    I m sure the CEO of Pimlico ( Charlie Mullins ) would be pleased to get involved so you have a happy ending(y)
     
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  12. ianmcd

    ianmcd

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    There is no expansion vessel in that pic ? this is a pic of an expansion vessel
     
  13. Marconar

    Marconar

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    Yes there is one of course
     
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