Evohome cycle rate and other settings

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  • Fly100
    Automated Home Jr Member
    • Sep 2018
    • 29

    #16
    Sorry for long delay, busy day. Here are the pics as requested.IMG_2094.jpgIMG_2095.jpg

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    • bruce_miranda
      Automated Home Legend
      • Jul 2014
      • 2307

      #17
      So that confirms you have no Boiler relay. So what is firing your Boiler?

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      • Fly100
        Automated Home Jr Member
        • Sep 2018
        • 29

        #18
        Originally posted by bruce_miranda View Post
        So that confirms you have no Boiler relay. So what is firing your Boiler?
        BRd91 ? there are 2 one for the Heating other for the water.

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        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #19
          So this means that if you have no Boiler relay or Zone Valves configured in the Evohome, you can't change the relay parameters. Your CH and DHW relays will be using the default TPI parameters that you cannot change. I new one for me.

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          • Fly100
            Automated Home Jr Member
            • Sep 2018
            • 29

            #20
            Originally posted by bruce_miranda View Post
            So this means that if you have no Boiler relay or Zone Valves configured in the Evohome, you can't change the relay parameters. Your CH and DHW relays will be using the default TPI parameters that you cannot change. I new one for me.
            I have noticed a little short cycling. Approx 8 mins between boiler firings.

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            • bruce_miranda
              Automated Home Legend
              • Jul 2014
              • 2307

              #21
              OK, but because you are using the micro switches of the CH and DHW valves, you have no parameters available to change that. The only way around that, is to add a 3rd BDR91 configured as a Boiler relay that then controls the boiler. Evohome will then expose the Relay parameters that you can then adjust. You will need to disconnect the micro switches from triggering the boiler.
              P.S. I wonder what happens if you simply bind a Boiler relay but don't actually connect it to the boiler. Evohome will make the relay parameters visible which then when set (I think) affect all relays. That might be also worth trying. All you will need is a powered up BDR91.

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              • Edinburgh2000
                Automated Home Guru
                • Dec 2016
                • 134

                #22
                Originally posted by Fly100 View Post
                I have noticed a little short cycling. Approx 8 mins between boiler firings.
                I don't think that "short cycling" can be anything to do with the Evohome controls or TPI. If you have not configured a boiler relay or any zone valve, then Evohome is not applying TPI control to anything. That is why it does not show the parameters - because you are not using TPI. The "short cycling" you see must be a function of your boiler's controls, reacting to changes in the flow rate and temperature.

                Does your "short cycling" match changes in the BDR91 states (i.e. green light on and off)? I suspect not but I am very happy to be put straight.

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                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #23
                  TPI is built into the BDR91, you cannot get around it. The screens just allow you to vary the default TPI parameters.

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                  • Edinburgh2000
                    Automated Home Guru
                    • Dec 2016
                    • 134

                    #24
                    Originally posted by bruce_miranda View Post
                    TPI is built into the BDR91, you cannot get around it. The screens just allow you to vary the default TPI parameters.
                    Indeed. But a BDR91 only performs TPI to the instructions it is sent by the Evohome controller (i.e. % output). All BDR91s are identical but, for example, those configured to control Hot Water never perform TPI, because the controller does not instruct them to do so. The hot water demand is either 100% or 0%.

                    I suspect that Fly100's configuration has no BDR91 that is set up to receive TPI instructions from his controller and so neither of his BDR91s will be performing TPI.
                    Last edited by Edinburgh2000; 5 February 2021, 11:11 AM.

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                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #25
                      The controller doesn't send anything other than Heat Demand to the BDR91. Its the BDR91 that then decides how to work based on that Heat Demand instruction. It either uses its default TPI parameters or the overridden ones.
                      The BDR91 can bind itself to the controller using several internal modes. Only the DHW mode performs no TPI. All the others perform TPI. The newest BDR91T can also be bound as a Heat Pump control and even that needs to switch of, by default, once per hour.

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