EvoHome - adding HW kit to combi boiler

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  • jonn
    Automated Home Jr Member
    • Apr 2011
    • 16

    EvoHome - adding HW kit to combi boiler

    Hi

    I've currently got EvoHome setup with just radiator / heating control, with hot water controlled by the built in timer on our Worcester oil fired boiler. The battery has packed up on the WB timer, so every time we have a power cut it reverts to defaults and we get heat / hot water at random times.

    I'm looking to add HW control to the EvoHome, and therefore do away with the built in timer entirely. As it's a combi type boiler, I don't need the hot water temperature controls, really all I need is the boiler relay on/off at set times functionality - so most of the bits that come in the hot water kit don't appear to be needed, just the BDR-91.

    Can I get away with just buying an additional BDR-91, or do I have to buy the HW kit (at double the price!) for some of the other components?

    Thanks!

    Jon
  • Dan_Robinson
    Automated Home Ninja
    • Jun 2012
    • 347

    #2
    This won't work.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

    Comment

    • jonn
      Automated Home Jr Member
      • Apr 2011
      • 16

      #3
      So the only option is to buy the full HW kit?

      Comment

      • top brake
        Automated Home Legend
        • Feb 2015
        • 837

        #4
        Originally posted by jonn View Post
        Hi

        I've currently got EvoHome setup with just radiator / heating control, with hot water controlled by the built in timer on our Worcester oil fired boiler. The battery has packed up on the WB timer, so every time we have a power cut it reverts to defaults and we get heat / hot water at random times.

        I'm looking to add HW control to the EvoHome, and therefore do away with the built in timer entirely. As it's a combi type boiler, I don't need the hot water temperature controls, really all I need is the boiler relay on/off at set times functionality - so most of the bits that come in the hot water kit don't appear to be needed, just the BDR-91.

        Can I get away with just buying an additional BDR-91, or do I have to buy the HW kit (at double the price!) for some of the other components?

        Thanks!

        Jon
        the hot water kit is for control of vented or unvented hot water cylinders

        Not possible to use this on a combi boiler
        I work for Resideo, posts are personal and my own views.

        Comment

        • jonn
          Automated Home Jr Member
          • Apr 2011
          • 16

          #5
          Originally posted by top brake View Post
          the hot water kit is for control of vented or unvented hot water cylinders

          Not possible to use this on a combi boiler
          Is there any solution? I would have thought turning a BDR-91 on and off on a HW schedule would be easy to implement...

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            I wonder whether adding the DHW kit but leaving the temp sensor in free air would work. In theory it should leave the hot water relay open permanently during the scheduled hours.

            Expensive way to do it though. Also, I can't understand why, if your boiler works in a combi-like way (i.e. hot hater heated on demand) you'd even want to put it on a timer?

            P.

            Comment

            • jonn
              Automated Home Jr Member
              • Apr 2011
              • 16

              #7
              Originally posted by paulockenden View Post
              I wonder whether adding the DHW kit but leaving the temp sensor in free air would work. In theory it should leave the hot water relay open permanently during the scheduled hours.

              Expensive way to do it though. Also, I can't understand why, if your boiler works in a combi-like way (i.e. hot hater heated on demand) you'd even want to put it on a timer?

              P.
              It's sort of like a combi - there's a small tank inside the boiler which is kept up to temperature when the DHW is turned on, but as soon as you open up a hot tap the boiler kicks in like a combi would, so the water isn't truly heated on demand. If you leave the DHW turned on all the time it will fire every now and then to keep the small tank up to temperature.

              I'll have a think about what you say about the DHW sensor left in free air - while the hot water kit is £80 vs. £40 for a BDR, it's not that much more than an external programmer would be...

              Comment

              • paulockenden
                Automated Home Legend
                • Apr 2015
                • 1719

                #8
                The advantage over an external timer is that you'd have app-based control, too.

                The only bummer would be if Honeywell added functionality which noticed that the HW temp wasn't rising and raised an alarm.

                P.

                Comment

                • The EVOHOME Shop
                  Site Sponsor
                  • Dec 2014
                  • 483

                  #9
                  I have done this on a Worcester Heatslave in the past and do a simailar thing on my buffer cylinder at home... Its not a recognised Honeywell application, but you could get this to work (but you will need the HW Kit).

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #10
                    Does the HW kit have any equivalent of frost protection that might kick in if the temperature sensor shows a value of less that a certain amount.

                    Comment

                    • Edinburgh2000
                      Automated Home Guru
                      • Dec 2016
                      • 134

                      #11
                      Originally posted by bruce_miranda View Post
                      Does the HW kit have any equivalent of frost protection that might kick in if the temperature sensor shows a value of less that a certain amount.
                      This thread suggests that it does.



                      and, if you are a subscriber to the Evohome forum, further confirmation here:

                      Last edited by Edinburgh2000; 29 September 2017, 10:55 PM.

                      Comment

                      • bruce_miranda
                        Automated Home Legend
                        • Jul 2014
                        • 2307

                        #12
                        In which case that is something else to bear in mind if leaving the temperature probe hanging in free air.
                        I know that before I was using the boiler demand feature of evohome, I was using an old hr80 to measure outside temperature. can't do that when you have boiler demand.

                        Comment

                        • Edinburgh2000
                          Automated Home Guru
                          • Dec 2016
                          • 134

                          #13
                          Originally posted by bruce_miranda View Post
                          In which case that is something else to bear in mind if leaving the temperature probe hanging in free air.
                          Probably simpler to throw the probe in the skip and short out the contacts of the CS92 with a resistor of about 6 kOhms.

                          (Resistance quoted from this link:
                          http://theevohomeshopforum.co.uk/vie...3ef521113a88f4)
                          Last edited by Edinburgh2000; 30 September 2017, 09:32 AM.

                          Comment

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