OpenTherm VR33 and Vaillant ecoTEC plus 428

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  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #46
    Care to share your circuit and code?

    Comment

    • Vikings
      Automated Home Sr Member
      • Jan 2021
      • 55

      #47
      I'm just using the circuit shown here https://ihormelnyk.com/Content/Pages...chematic_o.png and also the same here https://registry.platformio.org/libr...raus/Opentherm
      The code is using the J Praus opentherm library and I've based my code on his example. The only real change was to add a timeout into his 'conversation' handler so that it would reliably detect if the boiler didn't respond.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #48
        I'm guessing this interface can only monitor the OT traffic, it cannot actually inject or alter a command? That would require a gateway?

        Comment

        • Vikings
          Automated Home Sr Member
          • Jan 2021
          • 55

          #49
          No I'm using it to generate OT messages into the boiler (VR33 interface) e.g. set feed temperature and also to query data e.g. feed and return temperature. So it's acting instead of a thermostat.

          Comment

          • Vikings
            Automated Home Sr Member
            • Jan 2021
            • 55

            #50
            I've been trying this out but I'm having some problems.
            Whilst the loop is applied to the VR33 OT connections then the boiler works fine in response to the 240V demand signal as it always did.
            When I connect the OT up to my Arduino and start sending commands I can see the boiler is receiving the feed temperature control correctly but it never fires up. It seems to be ignoring the demand signal.
            I had initially not been sending the OT slave config message so I thought perhaps that was an issue so included that with the ch_enable bit set to 1. Still no change though.
            As soon as I put the loop back on then it fires up correctly.
            Any thoughts what might be wrong?

            Comment

            • Vikings
              Automated Home Sr Member
              • Jan 2021
              • 55

              #51
              Originally posted by Vikings View Post
              in response to the 240V demand signal
              Just to be clear that's the 'terminal 4' demand signal.

              Comment

              • Vikings
                Automated Home Sr Member
                • Jan 2021
                • 55

                #52
                Do you think I need to do anything with terminals 7-8-9 on my boiler? At the moment there is nothing connected but I wondered if I need to loop any of these to make it fire up.

                Comment

                • Vikings
                  Automated Home Sr Member
                  • Jan 2021
                  • 55

                  #53
                  I've just spotted an error in my code. I was sending the SLAVE_CONFIG message instead of STATUS. I'll give it another try later and hopefully that might fix the issue.

                  Comment

                  • Vikings
                    Automated Home Sr Member
                    • Jan 2021
                    • 55

                    #54
                    I've confirmed it's working correctly now. Sending the STATUS message with ch_enable set to 1 is what it needed. The demand control into terminal 4 is working fine alongside the OpenTherm temperature control. Sorry for the false alarm on this.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #55
                      I had to use terminal 7-8-9 in order to get my OTB to fire the boiler. And because that is undocumented, until I figured it out, I had to use the 240V trigger to fire the boiler and my VR33/OTB were simply handling the variable target flow temperature.

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