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Thread: Evohome underfloor heating setup

  1. #1
    Automated Home Jr Member
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    Default Evohome underfloor heating setup

    Hi, I have just had wet underfloor heating installed and added to my existing heating system, the plumber has installed a Polypipe ZRU PB970028 connected to a BDR91 and a evohome room temp sensor. I am just trying to switch everything on but wanted to check the settings to use.

    In the settings on the Evohome controller I have connected the temp sensor, all good but the valve I am unsure to select which heating type, mixing or zone valve? If I try to bind as a zone valve the BDR91 connects but if I try mixing valve it does not bind.

    I am also unsure if this setup is correct as I am unsure if this valve opens and closes but I am sure someone can advise.

    Any help would be appreciated.

    Mark

  2. #2
    Automated Home Jr Member
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    No need to reply, figured it out thanks to the Evohome Shop YouTube on how to wire a BDR91, it appears the electrician did not put the link wire between the second live and A terminal so the BDR91 had no power to give the pump.

  3. #3
    Automated Home Legend
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    Now get ready to get frustrated with the BDR91 and its inbuilt TPI. It will keep switching the UFH pump on and off several times an hour, which is quite undesirable for an UFH system. What you might want to consider doing is wire a pump overrun timer in parallel to the BDR91 set to about 30mins. That should keep the pump running between TPI cycles but then switch things off, when the heating schedule finally switches off albeit 30mins later. My UFH pump is adaptive too and takes about 5 mins to ramp up, and if yours is similar you will get frustrated sooner.

  4. #4
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    Thanks for the reply, I have not really noticed this tbh. What timer would you recommend and did you connect direct to the pump or to the BDR91? Thanks Mark

  5. #5
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    My UFH has its own motorised zone valve. So the BDR91 was connected to the zone valve. The microswitch inside the zone valve would power the pump. This was to ensure the pump would only run after the valve was opened. But in theory you could connect the BDR91 directly to both the pump and valve together.
    You need to look at CH pump delay timers, these used to be needed to keep the CH pump over running after the boiler had shut down. Modern boilers tend to have a pump output and so handle the overrun themselves.
    And what you do is wire the BDR91 to trigger the pump overrun timer, which in turn triggers the UFH pump. This ensures that while the BDR91 is busy doing TPI, the UFH pump keeps running between the off cycles. And then finally turns the UFH pump off after the last overrun.

  6. #6
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    Is this how it works?. During the off cycles, the boiler circ pump & the UFH manifold pump are running (with the UFH zone valve open).

  7. #7
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    With UFH, what you want is that the UFH pump stays on for as long as possible during the entire heating schedule. But what a BDR91 will try and do is keep turning on and off several times an hour. You don't want that.

  8. #8
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    Thanks, understood, but the TMV will demand full flow from the boiler circuit and none from the UFH recirc due to the mixed temperature reduction so probably requires boiler circ pump running as well to supply the manifold pump which I think is what you infer?.

  9. #9
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    The boiler's pump will almost certainly be running anyway because that will have an over run on it. But an UFH pump will normally just pump round the manifold, as long as the manifold outlets are open and are not using power actuators. You do not want the UFH running against closed outlets.

  10. #10
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    Once the HW supply temperature falls to the mixed flow temperature then the UFH pump will be supplied only from here, it will pump it through the UFH loops and return it all to the boiler so boiler circ pump best required although the UFH pump alone may give sufficient circulation on its own?.

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