Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

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  • mtmcgavock
    Automated Home Legend
    • Mar 2017
    • 507

    Originally posted by mdurkin View Post
    Hi - yes I think I could wire with a couple of options to achieve hot water priority, power the other two BRD91s (UFH and heating) from the C port on the Hot water BRD91, or I think similarly there's a 2 way switch in the motorised valves that I could wire in a similar fashion (I think) - just wondered if evohome could just implement this in logic - pretty easy - was a bit surprised not to see it.

    One other thing - my UFH is just off a BRD91 - just a zone valve. When the UFH comes on evohome opens the UFH zone valve as expected, but it also opens up the heating zone valve. Is this expected? I don't have the heating BRD91 double bound - I cleared it and rebound. Unless perhaps it's in the evohome controller where the binding is incorrect.
    I was thinking that perhaps once a zone valve is set for 'heating' in the water kit configuration, it gets opened for any heating requirement - the TRVs calling or the UFH zone?

    thoughts?
    Matt
    Yes I have the same problem, although with a towel rail circuit. I have it set up in the same set up as you, when my Towel rails call for a demand the heating zone & Boiler Relay BDR91 calls for a demand also. Although in my case this isn't an issue as all my radiators have HR92s, so therefore the heat can't go anywhere.

    I'm suspecting that the update later this year which allows you to have an 'Electric UFH' zone will just be the ability to open the BDR91 for that zone and not request a heat demand from either the heating zone valve or boiler relay. Which in that case would be brilliant to solve this issue (As you can then just use the S/L from the Microswitch to fire the boiler instead of boiler relay - however this would only be the case if you weren't using OT)
    Last edited by mtmcgavock; 26 November 2017, 11:15 PM.

    Comment

    • mtmcgavock
      Automated Home Legend
      • Mar 2017
      • 507

      Originally posted by HenGus View Post
      That depends, or so I was told, on what is needed by the boiler to ‘inform’ the boiler of a hot water demand. Atag requires a 3 way diverter valve. This was a compromise/ cheaper way of avoiding the need to re-pipe the heating system from an original ‘S’ Plan.
      I'm not sure whether that would make any difference, seeming really what you are currently doing is the same thing? It's just shutting and closing valves. My way is just the same as yours in theory (One opens and the other shuts). Whether this be with a boiler relay or OT bridge.

      However i'm unfamiliar with Atag, so unless they have some form of HW demand box (Like Viessman to go to max mode) i'm not sure what difference it would make.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        Any CH demand will open the CH valve, be it HR92s or UFH. Hence why you don't really need a CH Valve.

        In the Vaillant boiler, the controller send a Heat Demand message which tells the boiler what it is heating CH or HW. If you don't use a Vaillant controller the boiler works in CH mode only. The OT Bridge + VR33 never set the HW demand message. To work around this I use Domoticz + an eBUS interface that I built to provide a higher flow when heating HW and lower when doing CH only. Not ideal but works well.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          I too saw the OT Bridge fire the boiler in advance of the zone valves and didn't like that. Hence now my CH Valve is wired to the pump, which always comes on before the boiler is fired and stays open even during pump over run.

          Comment

          • mdurkin
            Automated Home Lurker
            • Apr 2010
            • 8

            Originally posted by bruce_miranda View Post
            I too saw the OT Bridge fire the boiler in advance of the zone valves and didn't like that. Hence now my CH Valve is wired to the pump, which always comes on before the boiler is fired and stays open even during pump over run.
            I’ve got to be honest, I’m pretty unimpressed with this behaviour. It’s not just in advance of the zone valves, it does it after the valves are closed as the zones shut down in the evening - I watched it this evening. It sat there with full demand via opentherm for a while with all the valves closed.

            I think my easiest option is to put back the ‘orange’ wire that is the feedback to the boiler (to pin 4 from memory) and remove the jumper on 3 to 4. This will shut off the boiler when no valves are open. I probably could find a switched output for the pump, but as my boiler is a system boiler, I don’t really want to looking for something that is designed to be self-contained within the boiler.

            I’ll probably put this back in place. Later when i get time I might wire a hot water priority - right now I see little modulation of heat, so it’s heating the water effectively. I thought I had read that evohome modulates up the heat during hot water demand. If that is the case hot water priority would be better so that the tank is heated as quickly as possible before switching back to CH only (and presumably a lower demand via opentherm). Call me a cynic, but does this actually work (different opentherm temperature demand when there is hot water heating requirements)?

            Comment

            • mtmcgavock
              Automated Home Legend
              • Mar 2017
              • 507

              Originally posted by mdurkin View Post
              I’ve got to be honest, I’m pretty unimpressed with this behaviour. It’s not just in advance of the zone valves, it does it after the valves are closed as the zones shut down in the evening - I watched it this evening. It sat there with full demand via opentherm for a while with all the valves closed.

              I think my easiest option is to put back the ‘orange’ wire that is the feedback to the boiler (to pin 4 from memory) and remove the jumper on 3 to 4. This will shut off the boiler when no valves are open. I probably could find a switched output for the pump, but as my boiler is a system boiler, I don’t really want to looking for something that is designed to be self-contained within the boiler.

              I’ll probably put this back in place. Later when i get time I might wire a hot water priority - right now I see little modulation of heat, so it’s heating the water effectively. I thought I had read that evohome modulates up the heat during hot water demand. If that is the case hot water priority would be better so that the tank is heated as quickly as possible before switching back to CH only (and presumably a lower demand via opentherm). Call me a cynic, but does this actually work (different opentherm temperature demand when there is hot water heating requirements)?
              I also found this the case when using the boiler relay. I found that it was firing the boiler when there was no demand for long periods (up to 4 minutes) before and afterwards. See thread - http://www.wordpress-1219309-4387497...elay-behaviour

              I found as I had altered the Number of cycles and minimum on time that it was causing the boiler relay behave this way. After changing this I have found the issue seems to have reduced, and there only being a few seconds in delay between the boiler relay switching on and the heating valve BDR91 switching on.

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                Yes it does work and it was my Hybrid OT method before I figured out I needed a jumper at 7-8. Remove the jumpers from 7-8 and use the valves to fire the boiler between 3 and 4. The Target temperature will still be varied by the OT but the boiler will fire via the traditional method.

                Comment

                • nieldm
                  Automated Home Jr Member
                  • Jun 2016
                  • 12

                  ...any further thoughts?

                  Originally posted by paulockenden View Post
                  Depends how the vote goes in June, I guess. But as long as we remain in the EU then fitting a part imported from the Netherlands really shouldn't affect a warranty claim, and like Top Brake says it would be an interesting day in court if they decided to refuse a claim.
                  As I read this thread researching OpenTherm along with my new Valliant ecoTec 838/Evohome installation, I came across this post.

                  Wondering if anyone's views have changed on what the installation of a VR33 might do to my 7 year Valliant warranty or if, indeed, the VR33 is now available in the UK (my Googling may be off today, but a search only came up with the source in the Netherlands). I am guessing the answer is as clear as everything else in this, ahem, cluster****.....?

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    The VR33 is a part made by Vaillant. It's just not made available to the UK market.

                    Comment

                    • Technomorph
                      Automated Home Lurker
                      • Aug 2017
                      • 6

                      I am considering buying the OT bridge for my Evohome system, however I need assistance in determining if my boiler will be a goer. I have a Glow Worm Flexicom 30 SX. The following states that the boiler is unofficially compatible when using the correct VR33 module:

                      What is OpenTherm? Boilers Boilers – Unofficial Controls OpenTherm Boilers and Controls Shown below are a list of OpenTherm capable / compatible manufacturers and boilers. These OpenTherm Boi…


                      Further reading from the below article suggests that the compatible module will be a AWB OPENTHERM MODULE 0020036768.

                      Vaillant boilers and OpenTherm Vaillant does not support OpenTherm directly out of the box in the UK. In a few european countries, such as the Netherlands, OpenTherm is highly prevalent and used, s…


                      Can anyone confirm either way from the below image of the boiler's PCB if this is correct?

                      20190616_182808.jpg

                      Comment

                      • mcalm
                        Automated Home Lurker
                        • May 2022
                        • 5

                        Originally posted by bruce_miranda View Post
                        My boiler is a Vaillant ecoTec plus 438. My boiler seems to need a switched live to fire up.

                        I don't have dedicated terminals for a 24V RT and Burner Off. I just have two eBUS connectiions, 7-8-9 connections which are for the old 24V analogue thermostats that were never used in the UK. Vaillant tell me that for the boiler to understand any eBUS command I need to use the Vaillant wiring centre. I don't think that advice is entirely accurate because my Opentherm bridge is able to alter the target flow temperatures, just can't fire the boiler up as top brake and Stuart have been able to.

                        If I bridge 3 and 4 my boiler fires up even if I don't want it to. If I leave 3 and 4 unbridged then the boiler never fires up. So currently I use the terminal 4 to fire the boiler via the zone switches.

                        I thought I would get in touch as you have a good understanding of how to add the VR33 to Vaillant boilers.

                        I was looking to replace my old Potterton Supriema which is still working but now coming to end of life and I was planning to replace it with a newer 2020 Ecofit Pure 415 15kW boiler that has come my way from someone I know who purchased a new home and added a big extension and had to upgrade the boiler.

                        Before I try and order the VR33 OT bridge from NL, I thought I check on the forum to find out if it is compatible with the boiler and if you could point me to the thread where I can find the steps I need to take to get OT working along with information on suitable OT compatible thermostat/timer will work. Also does Weathercomp work with this setup. I have attached the pic of the boiler PCB.
                        Attached Files

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          The VR33 should work fine with your boiler. However you can't have OT and Weather Compensation. The VR33 has a lower eBUS priority than the Vaillant controls needed for Weather Compensation. So the moment you connect those controls, the VR33 is renders useless.

                          Comment

                          • mcalm
                            Automated Home Lurker
                            • May 2022
                            • 5

                            Thank you for your speedy reply. Yes, I recall reading in one of your threads about the priority with the eBUS. I must admit I didn't realise the WC is simply a thermistor measuring the outside temperature and as a result it will take precedence. I take it when I plug the module in the control logic should detect it and won't need to figure out having to disconnect any jumpers or cables on the PCB?

                            I currently have a Glowwarm LCD Wall mounted thermostat that is connected to an old Salus EP200 timer. Other than Nest/Evohome which other thermostat/timer unit would you recommend. My current system is open vented but I am contemplating converting it to System and do away with the expansion and water tank in the attic. But my heating system is comprised of 22mm from the boiler and 10mm from the first floor and to it drops down to the ground floor. I'm mindful of the potential of leaks due to the pressurised system and I have carpetting above and in the living room downstairs. So I have been reluctant and been leaning towards keeping it simple and just do a boiler swap and get the benefits of OT.

                            Will I need to get the VR66 wiring centre if I go down the OT route? Just want to have all the items I need before I engage my heating guy whom I will have to handhold with regards to getting the OT setup. I can do the install/config myself but I took retirement from boiler work several years ago. Unfortunately, there is is very little if any enthusiasm for Opentherm within the installer community.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              Vaillant do the Weather Compensation in a very weird way. The actual external sensor is connected to boiler's PCB via a terminal block that is included with the VRC controller. So the external sensor itself doesn't render the VR33 useless. It is when you connect the VRC controller to the eBUS to make use of the external sensor does the VR33 not get detected. It sort of makes sense because you can have more than one controller on the bus. You don't need the Vaillant wiring Centre to use the VR33. But if you do use a Vaillant wiring centre then you can use a hack to have different Flow Temp max when heating HW or CH.

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