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Thread: Is my single zone UFH setup correctly?

  1. #1
    Automated Home Lurker
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    Default Is my single zone UFH setup correctly?

    Bear with me. Hopefully I'm worrying about nothing. Have had evohome for a few years but a new kitchen extension with UFH has left me confused.

    I've been running up the UFH in short bursts recently as the screed does its final drying (its been down 6 weeks). The 'problem' is that when the UFH is running (currently set at its minimum of 30 degrees) there is barely any temperature in the UFH return pipework. This appears to keep the boiler almost constantly firing whilst water also circulates our general radiator system. Doesn't seem quite right to me, even though heat is reaching the manifold and loops.

    As a background we have an unvented cylinder and radiator loop and in an S-plan arrangement. The UFH heating loop is tapped off the rad circuit and is providing 65 degree water to the manifold.

    We have the kitchen set up in evohome as a zone controlled by zone valve with Y87RF thermostat. Tweaks to the setpoint correctly open the UFH 2-port valve, which itself runs the UFH pump and heat is moved to where it needs to be.
    Not sure if this is right or not, but when the kitchen calls for heat, both the 'UFH' BDR and 'Heating' (radiators) BDR both light up.

    Do ask away with questions if thats too vague to answer!

  2. #2
    Automated Home Legend
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    Having the CH valve come on when the UFH is calling for heat is correct because the UFH is set up as a CH zone, so any demand in any CH zone will cause the CH valve to open. But none of that heat should make it to the radiators because they will all have their radiators valves.

    Do you have temperature probes on the manifold, flow and return? If 30C is going into the floor, what is the return coming back from the flow?

    Then if 65C is going into the manifold from the boiler, what is the temperature of the water going back to the boiler.

    You need to look at all 4 temperatures, to work out if you have a problem with the manifold valves not being open enough etc. It could easily be that your flow or return valves on the manifold loops are not opened enough.
    Last edited by bruce_miranda; 6th January 2021 at 02:25 PM.

  3. #3
    Automated Home Lurker
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    Ah ok. Well thats one concern knocked on the head then - thanks.
    The only reason our rads heat up is because only 3 out of 10 or so have HR92s on (we're mid renovation and so only convert a rad to evohome when we finish a room!).

    No, I've no temperature valves other than the incoming flow stat before the manifold pump. By touch the first of four loops is returning warm but the other longer loops are cool.
    Likewise I've no temp gauge for the boiler return but feeling it UFH circuit is cold, rad circuit is roasting. I suppose that 60+degree rad return mixes with the 20-degree ufh return and the boiler says "more heat needed". I've no idea what temperature differential the boiler looks for.

    Regardless, it sounds like I'm perhaps expecting too much from a (currently) stone-cold floor and pipework.

    Will keep an eye on it, and in the meantime I think some clip on thermometers are in order!
    Last edited by apkent; 6th January 2021 at 02:38 PM.

  4. #4
    Automated Home Legend
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    Infact its quite the opposite. 65C comes in and the manifold is actually hardly taking any of that in, so most of that is going back to the boiler. What is your room stat in the UFH zone set to? It could that the Heat Demand is still probably quite high, so the boiler is constantly being fired up to satisfy that, but your manually set 30C manifold is never letting it get there.
    Check the Heat Demand for the UFH zone as reported by the Evohome controller. Thwt should also give you some clues. Also open the manifold valves a bit more so that they all are equally warm.

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