Evohome Opentherm Boiler decision and set up

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  • 1animal1
    Automated Home Jr Member
    • Jan 2018
    • 39

    #91
    Actually, apologies, the Honeywell suggestion is a valve on the hot water side only for an Opentherm build. But I have a normally closed valve on the heating too so when the water heats up in summer, it doesn't feed the rads too

    Apparently this will be in the revised installation guide coming out soon according to their head of tech

    Comment

    • mtmcgavock
      Automated Home Legend
      • Mar 2017
      • 507

      #92
      Originally posted by 1animal1 View Post
      Actually, apologies, the Honeywell suggestion is a valve on the hot water side only for an Opentherm build. But I have a normally closed valve on the heating too so when the water heats up in summer, it doesn't feed the rads too

      Apparently this will be in the revised installation guide coming out soon according to their head of tech
      So basically you've got a standard S plan. So if you want to stop overshoots when your HW is reheating it's easy. Just wire the BDR91 for the CH motorised valve as follows (Assuming you've got 3 BDR91s, a CH, HW and Boiler Relay). From the C Port on the HW BDR91 take a wire to the A port on the CH BDR91. This will then give you HW priority. So when the HW is off or Heated up the BDR91 for the CH valve get's power to the A port. If there's a demand on the CH the BDR91 will close opening the MV.

      Comment

      • 1animal1
        Automated Home Jr Member
        • Jan 2018
        • 39

        #93
        What you describe I should already have... I'm using Opentherm so you don't use a BDR91 to fire the boiler. I have one BDR91 which is wired for the HW. The hot water valve is normally closed so when the heating is on, the is no power to the valves, so the flow will only go through the heating. When HW is requested and the BDR91 powers up, this opens the normally closed HW valve, and closes the normally open valve on the heating.... This is how Honeywell had my heating engineer wire it

        Comment

        • mtmcgavock
          Automated Home Legend
          • Mar 2017
          • 507

          #94
          Originally posted by 1animal1 View Post
          What you describe I should already have... I'm using Opentherm so you don't use a BDR91 to fire the boiler. I have one BDR91 which is wired for the HW. The hot water valve is normally closed so when the heating is on, the is no power to the valves, so the flow will only go through the heating. When HW is requested and the BDR91 powers up, this opens the normally closed HW valve, and closes the normally open valve on the heating.... This is how Honeywell had my heating engineer wire it
          Yes that makes sense, you'd said earlier on the Heating Valve was a NC valve not NO.

          Originally posted by 1animal1 View Post
          Actually, apologies, the Honeywell suggestion is a valve on the hot water side only for an Opentherm build. But I have a normally closed valve on the heating too so when the water heats up in summer, it doesn't feed the rads too
          And yes you are right i'd forgot you were using Opentherm, a Boiler Relay or Opentherm reciever does the same job in respect to that's what tells the boiler to fire instead of the Micro Switches from the valves.

          Well if that's the case then, I'm not sure why you're experiencing overshoots when reheating the hot water? Are you sure the Heating Valve is closing when HW demand is being requested.

          Comment

          • 1animal1
            Automated Home Jr Member
            • Jan 2018
            • 39

            #95
            I'll have to have a listen, see if there's flow....

            Difficult one isn't it, it should just be as straight cut, so that's the only thing it could be in theory. Although the heat cycle at the time of the overshoot was when downstairs was powering up for the morning. But all rooms were consistently over by 1-2C. Unless that's not a large enough shoot to worry about?

            Comment

            • mtmcgavock
              Automated Home Legend
              • Mar 2017
              • 507

              #96
              Originally posted by 1animal1 View Post
              I'll have to have a listen, see if there's flow....

              Difficult one isn't it, it should just be as straight cut, so that's the only thing it could be in theory. Although the heat cycle at the time of the overshoot was when downstairs was powering up for the morning. But all rooms were consistently over by 1-2C. Unless that's not a large enough shoot to worry about?
              I'd say that's a large enough Overshoot, especially if you are experiencing it every day. I tend to find all mine quite reliable (A mix using the HR92 sensors and remote sensors) some occasionally overshoot by 0.5 or 1 degree but not often.

              You should be able to tell if the Heating Motorised valve is closed or open on the little manual override lever on the valve when the HW is on.

              Comment

              • 1animal1
                Automated Home Jr Member
                • Jan 2018
                • 39

                #97
                Definitely worth digging deeper in that case.

                I would check the lever, but the normally open valve on the Heating doesn't have one. I did read the instructions when I sourced the parts and this is normal apparently.... I've tried to listen and feel the pipes, but this isn't telling

                Comment

                • DBMandrake
                  Automated Home Legend
                  • Sep 2014
                  • 2361

                  #98
                  Originally posted by 1animal1 View Post
                  I'll have to have a listen, see if there's flow....

                  Difficult one isn't it, it should just be as straight cut, so that's the only thing it could be in theory. Although the heat cycle at the time of the overshoot was when downstairs was powering up for the morning. But all rooms were consistently over by 1-2C. Unless that's not a large enough shoot to worry about?
                  If some zones are partially flowing maintaining a set point with a low heat output and other zones come on full to heat up to a set point some overshoot of the first zones can happen. This is because those first HR92's have adjusted their water flow rate for a low flow temperature to get room temperature equilibrium, then suddenly the flow temperature is going to maximum due to the demand from the other zones. Until the first HR92's sense a room temperature rise and react by closing down the room will overshoot a bit.

                  0.5C overshoot is typical in these conditions although I have occasionally seen 1C. Any more than this and I would suspect one of the following:

                  1) Maximum flow temperature set too high for the radiators/weather conditions.
                  2) Individual radiators in the problematic zones (if there are specific problem zones) over-speced compared to other radiators in the house.
                  3) Sticky or not fully compatible TRV valve bodies that are not allowing optimal control by the HR92.

                  I had issues with significant overshoot/oscillation in some of my rooms that turned out to be due to due to some cheap TRV valve bodies that had become "sticky". I replaced all the valve bodies with Valencia's and also ended up having to set them to stroke mode 1 (long story, covered by another thread) and after that the overshoots in a zone caused by another zone coming on full is less than 0.5C and most oscillation are gone or are very minimal compared to before.

                  I would try reducing the flow temperature a bit if you think it's too high. If that doesn't seem to help you could try setting the HR92's to stroke 1 mode - some valve bodies will work best with Stroke set to 0, some work best with stroke set to 1, it depends on the mechanical design of the valve and sealing washer inside.

                  If the stroke mode is set wrong for your valves the calibration between when the HR92 starts to call for heat from the controller and when it actually starts to allow water flow can be a long way out - this can lead the zone being prone to overshoot, among other things. Although I'm not sure if it's necessary, when I change stroke mode I always remove the HR92, turn the black wheel anti-clockwise and refit it to force it to do a re-calibration.
                  Last edited by DBMandrake; 25 December 2018, 10:19 AM.

                  Comment

                  • 1animal1
                    Automated Home Jr Member
                    • Jan 2018
                    • 39

                    #99
                    Morning chaps! Happy New Year....

                    After investigating this for the last few days, it seems me adjusting the ON time for the CH to coincide beyond the main CH morning warm up, has solved the issue. Temps throughout the day appear exactly where they should be with the odd 0.5 degree overshoot - so pretty happy. This must be related to the max temp water remaining in the system from the HW request, filtering into the HW, I can't think of anything else.

                    My only remaining question is, with my modified system having a 'normally open valve' on the CH and 'normally closed valve' on the HW - what happens if both the CH and HW request max heat within the same time slot - which does Evohome give priority to? Presume CH given my recent experience.
                    Last edited by 1animal1; 1 January 2019, 11:46 AM.

                    Comment

                    • HenGus
                      Automated Home Legend
                      • May 2014
                      • 1001

                      Originally posted by 1animal1 View Post
                      Morning chaps! Happy New Year....

                      After investigating this for the last few days, it seems me adjusting the ON time for the CH to coincide beyond the main CH morning warm up, has solved the issue. Temps throughout the day appear exactly where they should be with the odd 0.5 degree overshoot - so pretty happy. This must be related to the max temp water remaining in the system from the HW request, filtering into the HW, I can't think of anything else.

                      My only remaining question is, with my modified system having a 'normally open valve' on the CH and 'normally closed valve' on the HW - what happens if both the CH and HW request max heat within the same time slot - which does Evohome give priority to? Presume CH given my recent experience.
                      The system that I had in the house that I sold in July had an ATag is24 with OT control with hot water priority. The normally open CH valve closed whenever there was a HW heating demand. A HW demand would always result in a TMax Set flow temperature. CH would only demand TMaxSet when a zone/or zones were outwith their set temperature (c2C). Given your situation, I wouldn’t expect to see Evohome making an informed decision; ie, if there is a HW demand, I would have thought that TMaxSet will be demanded irrespective of any CH demand until HW re-heating is no longer required.

                      Comment

                      • 1animal1
                        Automated Home Jr Member
                        • Jan 2018
                        • 39

                        Thanks Gus, Firstly apologies, I have just seen your PM from February explaining the same set up!

                        I agree with what you say, it would make sense for the HW to get priority, for the CH to take over once HW is no longer needed. My only concern is that when my HW had a 1hr 30 time slot every second morning, during the 'morning heat up' - the water didn't get hot at all, i was constantly 'boosting' via the controller. since taking this slot an hour prior - all seems to be good.

                        I'm also considering how this will all work with a UFH system - presume that the UFH would work in tandem with the CH given that the UFH valve will work independently.

                        Comment

                        • HenGus
                          Automated Home Legend
                          • May 2014
                          • 1001

                          Originally posted by 1animal1 View Post
                          Thanks Gus, Firstly apologies, I have just seen your PM from February explaining the same set up!

                          I agree with what you say, it would make sense for the HW to get priority, for the CH to take over once HW is no longer needed. My only concern is that when my HW had a 1hr 30 time slot every second morning, during the 'morning heat up' - the water didn't get hot at all, i was constantly 'boosting' via the controller. since taking this slot an hour prior - all seems to be good.

                          I'm also considering how this will all work with a UFH system - presume that the UFH would work in tandem with the CH given that the UFH valve will work independently.
                          Thinking about your problem a bit more, I recall having a lengthy conversation with my installer about the valve configuration needed to work with an Atag boiler. The Atag ONE controller only works on a modified ‘Y’ configuration: this was confirmed by Atag Support. Could this be your problem; that is, your HW valve is not triggering a HW boiler flow demand?

                          Comment

                          • mtmcgavock
                            Automated Home Legend
                            • Mar 2017
                            • 507

                            Originally posted by HenGus View Post
                            Thinking about your problem a bit more, I recall having a lengthy conversation with my installer about the valve configuration needed to work with an Atag boiler. The Atag ONE controller only works on a modified ‘Y’ configuration: this was confirmed by Atag Support. Could this be your problem; that is, your HW valve is not triggering a HW boiler flow demand?
                            Surely you wouldn't be using the Atag controller if you've got Evohome?

                            Comment

                            • HenGus
                              Automated Home Legend
                              • May 2014
                              • 1001

                              Originally posted by mtmcgavock View Post
                              Surely you wouldn't be using the Atag controller if you've got Evohome?
                              I have moved on from Atag/Evohome/OT. The Atag ONE controller uses the same Atag boiler EBUS as Evohome OT. The Atag ONE controller requires a 3 port diverter valve. The discussion that I had with my installer and Atag Support at the time was that a 3 port diverter valve was also needed for Evohome OT control on an IS boiler with an unvented cylinder. My installer’s compromise was a zone valve for HW, and an inline open valve for CH. The latter closed whenever the HW zone valve opened.

                              What I am suggesting is that it is possible the ‘system’ as configured is missing the ‘trigger’ for the boiler to go to TMaxSet if all the zones are at their set temperatures when there is a HW reheating demand. All I can say is that my HW priority system worked well with Evohome OT.

                              I may be well wide of the mark. My new home has an annoyingly noisy WB boiler with 2 simple TPI thermostats and TRVs. It’s one saving grace is that it appears to be a very efficient heating system with none of the complexity of Evohome.

                              Comment

                              • mtmcgavock
                                Automated Home Legend
                                • Mar 2017
                                • 507

                                Originally posted by HenGus View Post
                                I have moved on from Atag/Evohome/OT. The Atag ONE controller uses the same Atag boiler EBUS as Evohome OT. The Atag ONE controller requires a 3 port diverter valve. The discussion that I had with my installer and Atag Support at the time was that a 3 port diverter valve was also needed for Evohome OT control on an IS boiler with an unvented cylinder. My installer’s compromise was a zone valve for HW, and an inline open valve for CH. The latter closed whenever the HW zone valve opened.

                                What I am suggesting is that it is possible the ‘system’ as configured is missing the ‘trigger’ for the boiler to go to TMaxSet if all the zones are at their set temperatures when there is a HW reheating demand. All I can say is that my HW priority system worked well with Evohome OT.

                                I may be well wide of the mark. My new home has an annoyingly noisy WB boiler with 2 simple TPI thermostats and TRVs. It’s one saving grace is that it appears to be a very efficient heating system with none of the complexity of Evohome.
                                The only thing the diverter is doing is preventing the central heating being heated whilst there is a hot water demand. So by having what your installed fitted on your last system it's the same as a diverter. The 'trigger' or demand will come from the controller not the zone valve.

                                I think the issue with 1animal1 is that the NO heating valve that has been fitted is not closing when there is a HW demand.

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