Vaillant flow temperature control for HW

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  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #46
    Just checked this. Like I suspected, the Left hand CYL terminal is 230V Live. And the moment that 230V live reaches the Right hand CYL terminal, the boiler is put into DHW heating mode.
    So my solution should work for you. Just send your DHW timer Live output that is used to power your DHW valve (Brown wire) to the Right hand terminal on the CYL terminal block.
    Keep all your Orange zone valve wires as they are to fire the boiler.

    Comment

    • fezster
      Automated Home Sr Member
      • Dec 2017
      • 72

      #47
      Thanks for confirming Bruce. Just waiting on my VR66 and VRC 470f to try this.

      Another couple of questions, if I may, as you understand how ebus works very well:

      1. The user on diynot has a 428 boiler and says ebus (through the VR65) is able to fire his boiler even though terminals 3/4 are not linked. I thought ebus was an "override" system, where the boiler continually fires unless ebus tells it not to? How then is he able to get SL and ebus working together?

      2. In a standard all vaillant setup with a VR65. In the absence of any override, am I right in saying the boiler will fire for DHW whenever the CYL terminal calls for it? So the VR65 sends an ebus command to the boiler. However, if you add a vaillant VRC 4xx, it is able to set a HW schedule. So now the VR65 will only fire the boiler for DHW if it is within schedule and the CYL terminals are activated. How do the ebus commands work now?

      - does the VRC tell the VR65 when to fire the boiler?
      - or does the VRC override the command from the VR65 to the boiler?

      Sorry - for the long windedness of that question. Hope it made sense. Just intrigued on how this all works, not really relevant to what I am trying to achieve.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #48
        1. eBUS can do (atleast) two things. It can vary the required flow temperature and it can fire the boiler. In order to fire the boiler, it needs the terminals 3-4 linked. However if you do not link them and supply a switched live to Terminal 4, then eBUS simply handles the variable flow temperature required. In fact this is how I used my system for a while where eBUS was simply managing my Flow (D.9) The VR65 just adds another layer to this, i.e. it can tell the boiler if it's doing a CH or DHW reheat.
        2. In an all Vaillant solution, the CYL terminals are always linked because they go through the boiler safety thermostat. A VR10 is then inserted to tell the boiler how hot the water in the unvented cylinder is. You can vary how hot you want the water, by using the dial on the front of the boiler. The VRC then handles things like the schedule (and boiler firing). The eBUS system is an hierarchy system, so it can detect the presence of schedulers and controllers on the bus. So when a VRC is present on the eBUS, it handles the boiler firing as per it's own schedule. The VR65 doesn't fire the boiler in any case. It is always a thermostat or scheduler that does the actual eBUS boiler firing. Unless you are using a SL 230V timer. The added confusion is that the VRC, if inserted into the boiler panel acts only as a scheduler and handles weather compensation etc. But it doesn't act like a remote
        room thermostat.

        It's all a bit smart but that makes things super confusing too.

        Comment

        • fezster
          Automated Home Sr Member
          • Dec 2017
          • 72

          #49
          Originally posted by bruce_miranda View Post
          In order to fire the boiler, it needs the terminals 3-4 linked. However if you do not link them and supply a switched live to Terminal 4, then eBUS simply handles the variable flow temperature required.
          This is what I'm not getting. The guy on diynot is adamant that:

          1. Terminals 3+4 are not linked. He uses SL from his motorised valves to 4 for central heating only.

          2. The DHW motorised valve orange/grey is connected directly to CYL on the VR65. Ie. SL does *not* go to the boiler.

          I double checked with him on private message, as I was sure ebus only worked if RT terminals are bridged (either 24V or 230V) on newer boilers, or 3+4 on the older 4 series boilers, like ours (which his is).

          Yet he says the boiler still fires on DHW demand. Either ebus is working without 3+4 bridged or he's got it wrong (and somehow is supplying SL to boiler).

          Not that it matters tbh. Just intriguing. I've got way too much time on my hands being off work atm. Lol.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #50
            If the Orange wire from the DHW zone valve is indeed not connected the Terminal 4, and the guy is sure of it, then it could mean that eBUS uses a different boiler trigger when in DHW heat mode. But unless he can completely disconnect his Terminal 4, there is no way of proving that. He probably hasn't checked inside his wiring box, where it's absolutely normal to have all Orange wires connected together. Or he could also have a system where his DHW is also operating a second CH zone simultaneously, and it's that CH zone that is causing the boiler to fire. No way of knowing that. But I agree, it would be nice to know. Because that could help some people.

            Your post reminded me to make another post telling people how the VR65 does have a place even in the fancy world of Evohome/OT etc.

            Comment

            • fezster
              Automated Home Sr Member
              • Dec 2017
              • 72

              #51
              Hooked up the VR66 today - I think it's working!

              Just want to confirm though - how do you know the HW demand has been activated? I see the tap symbol flashing on the front display and d.22 Hot water demand = 1. And the boiler is in S.24.

              I thought d.5/d.9 would show 80 degrees, but they do not. They continue to show the lower flow temps dictated by the weather comp.

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #52
                D.22 = 1, means that HW mode has been activated. Plus you have the flashing tap, which means it's working.
                D.5 is just what the CH knob has been set to. I call that the Flow Clamp temperature
                And D.9 is what Flow Temperature has been requested. But both D.5 and D.9 are ignored in HW mode and you will see the boiler ramping up the Flow Temperature past the Clamp Temperature D.5 all the way to what has been set in D.78.

                Comment

                • fezster
                  Automated Home Sr Member
                  • Dec 2017
                  • 72

                  #53
                  Nice one - thanks for confirming.

                  So just to confirm for anyone else looking to do this, all that is needed to activate HW mode on the VR65/VR66 is provide a 230V live to the right hand CYL terminal.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #54
                    One day I will dream up a use for the zone valve and the NTC sensor outputs in the VR65....I mean they are just sitting there doing nothing at the moment.
                    Maybe I should hook up the VR10 to the NTC terminals and use it to monitor my ABV return temperature

                    Comment

                    • fezster
                      Automated Home Sr Member
                      • Dec 2017
                      • 72

                      #55
                      The VR66 is considerably bigger than I was expecting. And just like you said above, I was thinking "what a waste" - none of the functionality is being used except the HW ebus command being sent via a switch (!)

                      Comment

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