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Discuss Lukewarm 'hot' water - secondary heat exchanger already changed in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Neil Sutherland

    Neil Sutherland New Member

    Hi, I'm looking for help with a persistent problem. I have a Vaillant TurboMax Plus 837E combination boiler which appears to be in fine working order. However, it provides only lukewarm water to the taps and shower. To date three engineers have looked at it but failed to resolve the problem. The diverter valve appears to be working normally, closing the supply to the radiators when a tap is turned on. The boiler temperature remains stable at 60 degrees or higher. I have had the secondary heat exchanger replaced and there seemed to be an improvement immediately afterwards; but it proved short-lived. As things stand, we are able to get hot water to the en suite shower but only by opening a hot tap in the main bathroom. The tap then runs cold, but the shower is warm! It works, but is very wasteful of water. You'll understand that I'm reluctant to call yet another engineer without having some idea what is going on, so if you have any ideas for things to check I'll be most grateful. Thank you.
     
  2. Gasmk1

    Gasmk1 GSR

    Sis the hot water flow pipe from the boiler hot to touch, if it is your problem could be a faulty mixer tap allow cold into the hot.
     
  3. Neil Sutherland

    Neil Sutherland New Member

    Thanks for the suggestion. But no, the hot side pipe on the shower mixer is cold to the touch (unless the hot tap in the other bathroom is open).
     
  4. Rightjob1

    Rightjob1 GSR

    Turn off all your colds to fixtures in the house and run the hot on its own..if it works fine then you have a tap that mixing tthr hot and cold
     
  5. Darren Jackson

    Darren Jackson Plumber GSR

    We are trying to determine whether this is a boiler problem or a backflow problem with a TMV. The hot water pipe "directly" underneath your boiler as it comes out, does this pipe get hot to the touch when a hot tap is turned on?
     
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  6. jtsplumbing

    jtsplumbing Plumber GSR

    Possible problem boiler not going onto Max burn when hot water demand calling
     
  7. Neil Sutherland

    Neil Sutherland New Member

    Any hot tap on its own runs lukewarm, but I can get hot water in the en suite by running a hot tap in the main bathroom .
     
  8. Neil Sutherland

    Neil Sutherland New Member

    Yes it does; but the water isn't hot when it gets to the tap (unless a main bathroom hot tap is on at the same time. Does my head in!
     
  9. Neil Sutherland

    Neil Sutherland New Member

    Thank you all for chipping in your ideas - we'll get there eventually. I can't rule out some oddity in the pipework; when we moved in I found the toilet in the en suite had a hot water flush! We live in an old pub that was refurbished in 1995 by a small developer and I think he did some of the plumbing work himself .
     
  10. Rightjob1

    Rightjob1 GSR

    Did you turn the valves off to the tap as in turn the colds off and run the hot only..this will tell if there is a problem in a fixture of cold crossing into hot
     
  11. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    Forget individual taps for now .

    Just turn off the cold supply to the boiler , NO water should come out of any hot tap , if it does then you can start to try pin point which one
     
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  12. Neil Sutherland

    Neil Sutherland New Member

    That sounds like a good idea. Would I be right in thinking that what I need to shut off is the valve shown in the attached picture? Seems a bit stiff; is it just a matter of turning it 90 degrees?

    Cold supply.JPG
     
  13. Chalked

    Chalked Plumber GSR

    That’s it.
    An Allen key fits inside.
     
    • Like Like x 1
  14. Neil Sutherland

    Neil Sutherland New Member

    Aha! When I turn off the cold supply to the DHW heat exchanger and open a hot tap, water flows (pretty much as it would with the water turned on). Just to check the supply was truly off, I tried using the en suite shower with the bathroom hot tap open - that's what we usually do to get a hot shower (!) - and the shower ran cold (as it should). I think we're making progress - what's next? (Can't say how much I appreciate the help.)
     
  15. Chalked

    Chalked Plumber GSR

    You shower needs non return valves fitted to th hot and cold feeds to it. Mains cold is overcoming the hot, so you have a cold shower.
     
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Hot/Cold/Lukewarm water from combi boiler Plumbing Forum Aug 29, 2018

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