Water underfloor heating too hot - Any advice please?

Discussion in 'Plumbers' Talk' started by Nicci Goddard, Nov 15, 2019.

  1. Nicci Goddard

    Nicci Goddard New Member


    We had an extension built two years ago, and at the time the whole floor of our downstairs was dug out and we had water underfloor heating installed, then a liquid screed poured on top.

    My problem is that in order to get the air temperature in my house to 20c (the temperature we like it at), the floor temperature goes up to 30c, which is too hot for the engineer wood floor we are planning to lay in January. That wood floor does not support a floor temp of more than 27c.

    Our setup is:

    - Hetta Group 4 port manifold
    - Grundfos UPS2 25-40/60 pump
    - Blending value attached to manifold (unsure of make/model)
    - Ideal Vogue C40 combi boiler
    - Water temperature for heating is set to 47c on the boiler, and this is confirmed by the inline thermostat attached to the boiler side of the manifold.
    - Heating hot water pipe out of boiler as single output, then splits into two pipes, each pipe with its own Honeywell motorised value. Each of the two values are linked to their own room thermostat - One for the radiators and one for the underfloor heating.
    - Critically, the output heating water temperature from the boiler is the same for both the radiators AND the UFH, as both come out of the boiler from the same single pipe.
    - We have the blender value on the UFH manifold set to minimum temperature, which on our blender valve is the setting below 40c marked as "MIN".
    - The above setup results in a floor temperature of around 30c, and an air temperature of about 20c.

    I have tried setting the boiler heating hot water temperature to lower than 47c, eg down to 40c or 35c. This does indeed bring the floor temperature down, but the radiators are not hot enough to heat our house air temperature up to 20c on a cold day.

    Any thoughts/ideas would be greatly appreciated please.
    One thing that did occur to me is that our blender valve might be broken, and might not be blending?


  2. Hans_25

    Hans_25 Screwfix Select

    I'd take a look at the specfication of your UFH, as most UFH systems won't get the room up to a good heat on cold weather - their output is limited. You need to find the kw output of the UFH, say per meter then multiply by the floor area.
  3. Hfs

    Hfs Screwfix Select

    Change the blending valve or head to one that has lower control of temp.
    JustPhil likes this.
  4. rogerk101

    rogerk101 Screwfix Select

    All the blending valves that I've installed in under floor heating systems have been adjustable. I'm sure yours is too. Just adjust it down by 1 or 2 settings and see how it goes. It may be that your heating might have to start earlier to get the room up to temperature with the lower temps, but at least your wooden flooring won't get too hot. Mind you, I doubt that 3 degrees would make the slightest difference to your floor boards. It's not the max them that will cause them to fail ... it's big fluctuations in humidity and/or temperature that will cause them to split or cup.
  5. FlyByNight

    FlyByNight Screwfix Select

    My blending valve goes down to about 35 deg, if you allow for thermal gradient across the screed and pipe that will bring it down enough.

    You can run it with a much boiler water temp which will be enough for the radiators and to ensure any stored hot water gets above 65deg.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice