Vaillant flow temperature control for HW

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  • fezster
    Automated Home Sr Member
    • Dec 2017
    • 72

    Vaillant flow temperature control for HW

    I'd like to be able to run my CH at lower flow temperatures during the summer, but am restrained by the Unvented Cylinder (not Vaillant) requiring 70 degrees flow in order to satisfy the cylinder stat at ~60 degrees (to prevent legionella).

    I've looked at the various Vaillant controls available and whilst the VR65 seems to be able to achieve this, it doesnt cater for multiple heating zones.

    So the plan is to use an ebus adapter which takes the SL from the HW zone valve and adjusts the flow temperature on the boiler to MAX, reverting back to the set flow temperature once the HW zone valve closes.

    Has anyone done something similar? And any pros / cons compared to using the V65 and the supplied NTC?
  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #2
    Originally posted by fezster View Post
    I'd like to be able to run my CH at lower flow temperatures during the summer, but am restrained by the Unvented Cylinder (not Vaillant) requiring 70 degrees flow in order to satisfy the cylinder stat at ~60 degrees (to prevent legionella).

    I've looked at the various Vaillant controls available and whilst the VR65 seems to be able to achieve this, it doesnt cater for multiple heating zones.

    So the plan is to use an ebus adapter which takes the SL from the HW zone valve and adjusts the flow temperature on the boiler to MAX, reverting back to the set flow temperature once the HW zone valve closes.

    Has anyone done something similar? And any pros / cons compared to using the V65 and the supplied NTC?
    This is exactly how my boiler works with Evohome/Opentherm. Most system boilers will revert to a max flow temperature when hot water heating is required. That said, I would have thought that Evohome with the hot water kit and weather compensation would give you what you need. Other more knowledgeable contributors will have a view.

    Comment

    • fezster
      Automated Home Sr Member
      • Dec 2017
      • 72

      #3
      I don't have Evohome or the Opentherm bridge. Just a standard S-Plan plus setup, with upstairs, downstairs and HW zones. I've been reading up on a Raspberry PI setup with an ebus/usb adapter and controlled by ebusd: https://github.com/john30

      My thinking is to use the SL from the HW zone valve as an input into the pi and have the software send the relevant ebus command to increase the flow temp on the boiler. It seems like a common use case so I'd be surprised if someone hasn't already done this.

      Comment

      • dty
        Automated Home Ninja
        • Aug 2016
        • 489

        #4
        bruce_miranda has built something similar. He uses Domoticz to listen to what's going on in his Evohome and when the hot water is switched on he uses ebusd to alter the max flow temperature on his boiler. Provided you're comfortable with the electrical side of things (in particular, using a 240V AC input to an RPi) then this should be reasonably easy to build.

        Comment

        • fezster
          Automated Home Sr Member
          • Dec 2017
          • 72

          #5
          I think the VR65 or VR66 will achieve what I want, but not certain it can be used without the corresponding Vaillant ebus programmer / thermostat (i.e. VRT 360 or VRC 400).

          Would it be possible to link the HW zone valve SL to the CYL terminals, and will the VR65 then instruct the boiler via ebus to boost the flow temp whenever the CYL terminals are closed? Could anyone who has a VR65 without the vaillant controls confirm? Thanks.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #6
            A VR65 without a controller will kick the boiler into an 80C HW flow situation and keeps going because there is no controller to tell it to stop! I've tested this....

            You can do this without using a VR65 but you can't do this without a controller.
            Last edited by bruce_miranda; 10 December 2017, 08:22 PM.

            Comment

            • fezster
              Automated Home Sr Member
              • Dec 2017
              • 72

              #7
              Ah ok. Seems a bit nonsensical. I'd have thought once the CYL stat was satisfied, the VR65 would revert to the flow temp set on the boiler. Oh well - that would have been an easier solution to my issue.

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #8
                The way Vaillant have designed their boilers is that the DHW knob and function only works from a Vaillant controller and only when a VR10 NTC sensor is used. That sensor comes with the VR65 but has to be bought separately with the VR66. I worked out the eBUS command to get the HW knob to work but the problem is that I have the VR33 connected which shortly overrides anything I send on the bus. Also the OT Bridge doesn't use the two channels anyway, so it was a bit pointless.

                Comment

                • fezster
                  Automated Home Sr Member
                  • Dec 2017
                  • 72

                  #9
                  The NTC is only required if you want to control the cylinder temperature (using the HW rotary dial on the boiler). If you want your cylinder to be heated to the temperature on the cylinder stat, you only need to ensure the flow temp of the boiler exceeds this.

                  What's unclear is whether the VR65/VR66 will boost the flow temp to 80 degrees on HW demand *even if the CH rotary dial on the front of the boiler is set to less than 80*. Different people say different things, and I wonder if it differs based on firmware's. If the ebus can override the flow temp regardless of what's set on the boiler, then this would be a cheap and easy way to achieve independent HW flow temp control on vaillants.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #10
                    if you give me till the New Year I can test anything you want. I accumulated quite a lot of test gear and we have the same boiler with the new PCBs.

                    Comment

                    • fezster
                      Automated Home Sr Member
                      • Dec 2017
                      • 72

                      #11
                      That'd be great. TYVM

                      Comment

                      • Symbolics
                        Automated Home Lurker
                        • Feb 2019
                        • 6

                        #12
                        Originally posted by fezster View Post
                        That'd be great. TYVM
                        Just checking if anyone has found the answer to this? I have a Vaillant VR66 unit that provides a DHW signal to a Vaillant boiler via the ebus. It seems that the VR66 does not set the DHW temp, and the max I can set the temp via the boiler is a measly 65C. This is no good, I was hoping to get about 75.

                        Comment

                        • mtmcgavock
                          Automated Home Legend
                          • Mar 2017
                          • 507

                          #13
                          Originally posted by Symbolics View Post
                          Just checking if anyone has found the answer to this? I have a Vaillant VR66 unit that provides a DHW signal to a Vaillant boiler via the ebus. It seems that the VR66 does not set the DHW temp, and the max I can set the temp via the boiler is a measly 65C. This is no good, I was hoping to get about 75.
                          The 65oc is the temperature of the water not the flow temperature, not sure why anyone would want it any hotter than this? I find 55oc too hot at the taps.

                          Comment

                          • Symbolics
                            Automated Home Lurker
                            • Feb 2019
                            • 6

                            #14
                            Originally posted by mtmcgavock View Post
                            The 65oc is the temperature of the water not the flow temperature, not sure why anyone would want it any hotter than this? I find 55oc too hot at the taps.
                            My Vaillant is not a combination boiler.

                            I am using the Vaillant system to produce hot water to circulate in a Megaflo tank. I would like to keep the Megaflo at 60 degrees, to prevent Legionella. To achieve this efficiently I need to generate hot water using the Vaillant that is at 75 degrees, which is circulated inside the Megaflo and radiates its heat into the Megaflo.

                            If the Vaillant really as an arbitrary max of 65 degrees, then I might stop using the Vaillant for how water and re-deploy it as a secondary central heating boiler, and get a very simple boiler for hot water generation that has a simple dial on the front for setting the flow temperature.

                            Comment

                            • mtmcgavock
                              Automated Home Legend
                              • Mar 2017
                              • 507

                              #15
                              Originally posted by Symbolics View Post
                              My Vaillant is not a combination boiler.

                              I am using the Vaillant system to produce hot water to circulate in a Megaflo tank. I would like to keep the Megaflo at 60 degrees, to prevent Legionella. To achieve this efficiently I need to generate hot water using the Vaillant that is at 75 degrees, which is circulated inside the Megaflo and radiates its heat into the Megaflo.

                              If the Vaillant really as an arbitrary max of 65 degrees, then I might stop using the Vaillant for how water and re-deploy it as a secondary central heating boiler, and get a very simple boiler for hot water generation that has a simple dial on the front for setting the flow temperature.
                              You are mis understanding. The 65oc is the temperature of the water in the cylinder. When using the VR66 you have to use the Vaillant NTC probe into the cylinder. This then measures the temperature of the HW, which you set in your Vaillant controller, or on the front of the boiler. You then set which flow temperature you require for heating DHW in the Diagnostic menu along with what KW output you require for the cylinder.

                              Settings D.020, D.077 and D.078 is what you require.
                              Last edited by mtmcgavock; 3 February 2019, 07:09 PM.

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