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Discuss Thermodynamic box - cold water in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Mark Weightman

    Mark Weightman New Member

    Moved in to our house last year with thermodynamic pump on the hot water tank. It pretty much takes water from the top outlet of the hot water tank heats it up in the box and returns to the bottom of the tank. It worked fine but just had our boiler replaced and changed hot water tank to unvented. The box only cuts in after temp has dropped, it works correctly but my problem is when it’s running it ‘steals’ my domestic water which makes it cold at the taps/shower. Any advice or ideas that I could do to stop this happening. There are valves on the box and I’ve tried throttling them in but makes no difference.
    Thanks
    Mark
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    any pics of said box?
     
  3. Mark Weightman

    Mark Weightman New Member

    It’s underneath hot water cylinder

    A979AFC9-03A4-4B11-9E15-AC3492167DB2.jpeg
     
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    i would say your missing a check valve on the cold to the pump

    im guessing you have a panel on the outside

    also im guessing its teed in to hot outlet instead of the secondary port
     
  5. Mark Weightman

    Mark Weightman New Member

    Correct, the panel is on the side of the house as it’s a refrigerant gas it’s the ambient air that heats it.
    I’m sure there’s a non return valve inside the box. It’s doing the right job in that it’s circulating the water in the cylinder and heating it up, it’s just when I run a tap and as the box pump cuts in the hot water chooses to flow back through the box rather than to my taps. I’ve just been turning it off while showering and then back on after for now.

    99489DB0-019A-4264-99D7-7E9F61E08408.png
     
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    i would say needs to go into the secondary return port / connection

    also i would say the stat wire is in the wrong pocket
     
  7. rpm

    rpm Trusted Plumber Top Contributor!!

    So, was working fine then new hot water tank and boiler fitted now steals the hot water, surely it is not plumbed in correctly then.
     
  8. Mark Weightman

    Mark Weightman New Member

    I’m guessing so too but the plumbers who put in the new tank and boiler hadn’t seen the box before. I’ll get them back round to investigate but I’m just trying to find out any possible solutions.
     
  9. rpm

    rpm Trusted Plumber Top Contributor!!

    Does the pipework at the top of the cylinder match the drawing, it`s not shown in the photo.
     
  10. Mark Weightman

    Mark Weightman New Member

    The tee coming off to the left goes to the box, it comes down and to the right for domestic water.

    6D6A6F0C-0C0E-4CDF-AD2F-A5F5BD8EA412.jpeg

    AF7815BD-891A-4D59-9676-2E85B59AA7A5.jpeg
     
  11. rpm

    rpm Trusted Plumber Top Contributor!!

    Well not saying it is wrong however due to lack of headroom it is different. Perhaps someone else has a view on the way the pipes are done.
     
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