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Underfloor heating not working.

Discussion in 'Plumbing and Central Heating' started by sups, 4 Feb 2020.

  1. sups

    sups

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    Hello,

    Any help here would be appreciated,
    I have a vaillant ecotec plus 637 with a multi zone setup. The kitchen has underfloor heating and the rest of the house is using rads, I also have a megaflo water tank. I don't have a manifold I simply have a number of valves, one for the UHF, one for the Rads and one for the water tank.

    So far everything has been working fine (the setup is around 7years old) but over the past coupl of months I've noticed that the UHF isn't working right - in that only small patches of the floor get warm.

    I've tried flush out the whole system to try and understand If there are any blockages...there doesn't seem to be any, as I think I managed to empty the system without too many issues. After filling up and bleeding the system, the ufh still doesn't work. I've had a new pump installed just days ago thinking that it might help but unfortunately it didn't.

    One symptoms I'm noticing is that heating the rads or the water tank works fine, Ive set my boiler to 65 degrees. On demand the boiler goes up to 65 and stays there (or there abouts). But if I turn the UHF on only, the boiler goes up to 75 degrees, heat cuts off, the boiler temp then goes down to 40 before firing up again.... And the cycle repeats. This seems a bit odd and I don't recall it ever doing that before.

    I did have a major power issue back in Dec while I was abroad, a came back to a very cold home to find the mains fuse had dropped. part of me thinks that the boiler config could have gone back to factory settings, but then again the settings should be saved.

    Anyone here able to help me diagnose what could be happening. Pleeeeease?

    Thanks
    Sups

    Read more: https://www.diynot.com/diy/forums/plumbing/create-thread/preview#ixzz6D0DT4WA5
     
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  3. Chris_W

    Chris_W

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    ‘Sup sups (couldn’t resist sorry),

    Have you checked the zone valve (would be my first port of call, as everything else is working, and it seems to overheat when ufh selected.
     
  4. picasso

    picasso

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    You should have a blending valve as you would not want 65c water running through the ufh ,
     
  5. sups

    sups

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    Yea.. I do have a valve and it does work, 100% sure of that.
     
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  6. sups

    sups

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    Yes I do.. it's currently set to 60 degrees.. it works and I can feel the change in temp on flow port of the valve.
     
  7. picasso

    picasso

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    What happens if you turn off the rads and hot water and just have the ufh on, does the floor heat then ?
     
  8. sups

    sups

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    I get small areas of Luke warm floor.. but in this seceanario the boiler would go up to 75 degrees (way past the 65 that I have set) which then drops back to 40, then up to 75 to 40 and on and on..

    Another thing I failed to mentioned is that the return from the UHF never really warms up.. its always cold.. but I don't know if this is because the boiler keeps flip flopping between 75 and 40 degrees.
     
  9. picasso

    picasso

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    Its lack of circulation through the ufh circuit that's causing the boiler to cycle, if there is nothing other than the two port valve and blending valve then I reckon the blending valve if knackered.
     
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  11. sups

    sups

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    That's an easyish replacement.. but currently changing the knob between 60 degrees and 35 degrees, I can feel the difference in temperature on the flow port. Is that enough of a test to rule the valve out?
     
  12. picasso

    picasso

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    You sure the pump is facing the right direction? cant really help with no circulation through a keyboard,
     
  13. sups

    sups

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    Yes, the pump is the the right way.. Symptoms are the same with the new pump as with the old pump. Can't help feeling bad about folking out 90 quid for that pump..☹️
     
  14. picasso

    picasso

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    What setting do you have the pump on?
     
  15. sups

    sups

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    Currently on 3.
     
  16. picasso

    picasso

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    Then I would change the blending valve thermostatic head (if it separates) but cant guarantee that's your problem,
     
  17. rb1980

    rb1980

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    I had similar issues .one zone wouldn’t heat up even tho the return was warm.
    If your boiler is cycling like that it’s either a blockage or maybe airlock causing lack of flow . I didn’t have the boiler cycling issue but I ran some x400 through the system and 2 rooms that hadn’t heated up for a year now do . So I’d try that 1st as a cheap possible solution .
     
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