Boiler Relay control but only on main zone

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  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    Boiler Relay control but only on main zone

    Is it possible to have the Boiler Relay to work only with a single zone calling for heat? I have the main unit set up in an area without any radiators. I want to use the main unit like a general home thermostat. But I don't want all the radiator valve also to call for their own heat demand. Is that possible or is it all or nothing.
  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #2
    As the controller can be used to control temperature in a single zone, this should be possible. That said, if you have no intention of using the ability of Evohome to control up to 12 zones, Evohome may not be your best/cheapest control option.

    Comment

    • bruce_miranda
      Automated Home Legend
      • Jul 2014
      • 2307

      #3
      I am infact using the evohome to control 12 zones. However some zones are largely unused rooms. I dont want those radiator valve calling for heat simply because the temperature in those rooms dropped below the set point a little.
      What i need is for the boiler to fire up only if the main zone has dropped below the set point.

      Comment

      • ccourtney
        Automated Home Lurker
        • Feb 2016
        • 2

        #4
        Originally posted by HenGus View Post
        As the controller can be used to control temperature in a single zone, this should be possible. That said, if you have no intention of using the ability of Evohome to control up to 12 zones, Evohome may not be your best/cheapest control option.
        Although the cost of the Evohome system elements required to work a simple system in this configuration are pretty similar to the alternative products on the market eg Nest or Hive and at least it then does leave a lot of room for a future upgrade path to smart zoning should they wish.

        Comment

        • HenGus
          Automated Home Legend
          • May 2014
          • 1001

          #5
          Originally posted by bruce_miranda View Post
          I am infact using the evohome to control 12 zones. However some zones are largely unused rooms. I dont want those radiator valve calling for heat simply because the temperature in those rooms dropped below the set point a little.
          What i need is for the boiler to fire up only if the main zone has dropped below the set point.
          I have 12 zones set and I manage the problem by setting zone temperatures which I know will not cause the boiler to fire unless it is very cold outside.

          Comment

          • DanD
            Automated Home Ninja
            • Feb 2016
            • 250

            #6
            Hi,

            If I'm understanding correctly what you're trying to do, it sounds like you want the HR92s outside of the main zone to function more like conventional TRVs i.e. they just open and close to keep the room at the set point when the boiler is switched on by the main zone thermostat, with no control or feedback to the boiler. Is this what you'd like to achieve? If so, then the simplest solution would be to either unbind the HR92s or remove them altogether and revert to using the old TRV heads outside of the main zone. If you want to retain the ability of monitoring the temperature in each zone, but just remove the boiler control feature of the HR92, I'm not sure whether this is possible in the binding setup.

            Dan

            Comment

            • DBMandrake
              Automated Home Legend
              • Sep 2014
              • 2361

              #7
              Originally posted by DanD View Post
              Hi,
              If you want to retain the ability of monitoring the temperature in each zone, but just remove the boiler control feature of the HR92, I'm not sure whether this is possible in the binding setup.
              It's not possible. All bound HR92's will call for heat from the boiler via the controller when they need it - you can't exclude any unless you completely unbind them, at which point they now act like a standalone TRV that cannot be scheduled and do not even report room temperature back to the controller.

              So no, it can't be done. This is an often asked question because it also makes it impossible to have a zone that is an electric heater - for example you could use a DTS92 as the temperature sensor and a wireless relay configured as a "zone valve" to control an electric heater, which would work except for the fact that as well as turning on the electric element it would call for heat from the boiler via the boiler relay (a zone can't be excluded from turning on the boiler) thus end up running the boiler when no radiators are open, simply circulating hot water through the automatic bypass loop wasting gas.

              It would be such a simple feature for Honeywell to add, but they don't seem very inclined to make any major functional changes to the Evohome, only small refinements to existing features.

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #8
                So it's an 'All' or 'Nothing' Boiler binding then. That's a shame. I agree, in the set-up of HRxx it could have easily asked if Boiler control was required or not for that zone controller.

                Comment

                • paulockenden
                  Automated Home Legend
                  • Apr 2015
                  • 1719

                  #9
                  You /could/ make a little raspberry pi powered box to sit between your relay and boiler. It could check the current zone status (via the API), and if only that zone is below temp it could remove the boiler signal.

                  P.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #10
                    I know I could make something for this. But anything I make would be rely on an internet connection which doesn't appeal.

                    OK so currently my system uses HRxxs and the Evohome with no boiler relay. I still use my old wired time clock for the scheduling.

                    I am about to add a single zone underfloor heating and was planning to use the Y87RF2024 thermostat for the UFH so that I could integrate that with my Evohome. Will that mean that I will be moving to full system boiler interlock as a result. Or will the UFH boiler demand be separate from the rest of the system.

                    Comment

                    • The EVOHOME Shop
                      Site Sponsor
                      • Dec 2014
                      • 483

                      #11
                      Originally posted by bruce_miranda View Post
                      OK so currently my system uses HRxxs and the Evohome with no boiler relay. I still use my old wired time clock for the scheduling.
                      I assume you are using the 2 or 3 port option through hot water guided configuration instead of boiler relay?

                      Originally posted by bruce_miranda View Post
                      I am about to add a single zone underfloor heating and was planning to use the Y87RF2024 thermostat for the UFH so that I could integrate that with my Evohome. Will that mean that I will be moving to full system boiler interlock as a result. Or will the UFH boiler demand be separate from the rest of the system.
                      What is your current heating system configuration? Are you planning on adding this UFH circuit to your existing radiator heating circuit? Why do you think you haven't got boiler interlock currently? Only way you wouldn't have boiler interlock is if the HR92's were bound to evohome just as a HR92 controller only.

                      Comment

                      • bruce_miranda
                        Automated Home Legend
                        • Jul 2014
                        • 2307

                        #12
                        I have a normal S plan system. With a time clock that controls both the hot water and central heating. I then have an Evohome with the TRV controllers. There is no boiler relay connected. I simply use the Evohome to control the TRVs and get feedback on the temperatures in each zone. The boiler is still timed via the old time clock.

                        Now wet UFH is being added to the radiator system. The UFH is going to be controlled by a Honeywell Y87RF2024 Single-Zone Thermostat. The reason for that choice of thermostat was to register it to the evohome as one zone. But the Y87RF2024 comes with it's own Relay unit. In adding the Y87RF2024 to the Evohome, will all the TRV controllers also demand heat via the Y87RF2024's relay box?

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #13
                          I suppose I could have done this. Use the Evohome's internal sensor and the BDR91 as the actuator for that zone. That way the BDR91 is triggered only via that zone.

                          Comment

                          • Nairnw
                            Automated Home Lurker
                            • Nov 2015
                            • 9

                            #14
                            I might be going off on a tangent here but why not pair you main zone to a secondary Evohome Controller? Pick up an older one after someone has upgraded and use it, while keeping the other one setup for your other 12 zones. 12 is the limit per controller anyway.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #15
                              That wasnt what I wanted to do. I didn't want all zones calling for heating except the main zone. I knew that if I registered the BDR91 as a System Device boiler interlock then all zones would make the boiler fire if they fell below the set point. What i hadnt appreciated was that I could use the evohome's internal sensor in the main zone and have the bdr91 setup as the accutator for that zone. That way only the main zone would call the boiler if it needed heat.

                              Just a little too late. I didnt need to buy a Y87RF for my underfloor. I could have just used the evohome controller for that zone paired with its own bdr91.

                              Anyway hope this helps someone else.

                              Comment

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