Opentherm with Evohome

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  • sandyman
    Automated Home Sr Member
    • Mar 2016
    • 85

    #16
    Originally posted by HenGus View Post
    Thanks - scratches head! Are you saying that the Evohome HW kit will not do the same thing; i.e., sensor demands heat which via Evohome sends demand to BDR; motorised valve opens and boiler comes on. Is this problem unique to Viessmann? Opentherm is looking less attractive than it was.
    right up to a point. the evo hot water kit is a necessary part of the system regardless of how you do the rest: HW sensor demands , HW zone valve opens, sends demand to boiler, boiler comes on. question then is what is the flow temp of the boiler?

    DHW needs a really hot flow (70 plus) to recharge the cylinder quickly to 60. My experimental evidence shows that (at least for viessman) the boiler tries to keep flow and return 20 degrees apart - but if the return gets too warm, it shuts the boiler down, there is an inbuilt limiter. what then happens in practice is that your cylinder with a target temp of 60 degrees never gets to target because the boiler keeps shutting off. it interprets return@ close to 60 degrees (which is what it will be , as your cylinder approaches 60) as "gosh the system is too hot, I better shut down". So the viessman hot water kit is to be used AS WELL AS the honeywell one - they do different things. The honeywell evo one controls the zone valve and talks to the controller. The viessman one is there purely to tell the boiler "the demand now is for hot water, so ignore your "return too hot" limiter, and just give it full whack until told otherwise".

    I think its almost a generic problem with condensing / low temp target system boilers (certainly for viessman 100) and DHW. You do not get any different behaviour with an evo boiler demand BDR instead of an OT bridge (I know, I have had both on the exact same boiler and system).

    I had hoped that the evohome OT bridge / OT protocol would have some additional smarts that could tell the boiler "actually the demand now is HW, please do the right thing", but it appears not.

    others on here may have different experience with their hot water cylinder reheat behaviour if they have different system boilers (might have a different behaviour with high return temp), I can only speak for the way my viessman 100 behaves.

    viessman cylinder demand terminal box wiring details http://www.viessmanndirect.co.uk/fil...inal%20Box.pdf
    It doesn't cost a lot (compared to new boiler and all the work!) think it was order of 100 quid.

    oh and there's one more option with viessman if you have the option to change your plumbing - 4 pipe. separate flow/return circuits for CH and HW, can run them at different temps thus achieving the same as I have described but on separate circuits. I'm not the expert, just read about it. This was not an option for me due to the physical layout requirements (can you run more flow/returns in the right place?), talk to your installer..
    Last edited by sandyman; 15 October 2016, 07:08 PM. Reason: added viessman kit link

    Comment

    • HenGus
      Automated Home Legend
      • May 2014
      • 1001

      #17
      @sandyman Thanks again.

      Comment

      • DanD
        Automated Home Ninja
        • Feb 2016
        • 250

        #18
        Hi,

        others on here may have different experience with their hot water cylinder reheat behaviour if they have different system boilers (might have a different behaviour with high return temp), I can only speak for the way my viessman 100 behaves.
        Just to confirm that I've had exactly the same problem. I've previously posted about my Glow Worm Ultracom system boiler which doesn't have any way of separating the DHW demand from the CH demand when connecting an Evohome system. It took me quite a long time to work out that the boiler was modulating its flow temperature which prevented the DHW hitting its target temperature. The only solution for me was to set the CH target temperature high enough on the boiler to meet the DHW requirement. Prior to my Evohome install I used a Glow Worm external controls module for the boiler which did separate the two types of demand, but this module could not be linked to the Evohome system .

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #19
          My own Vaillant 438 ecotech open vented boiler works ok. it is supposed to be capable of handling two different temperatures but only when used with Vaillant's own controls. So currently my HW knob on the boiler does nothing.
          Using the Evohome and the Opentherm bridge, the OT just kicks the boiler into a 90C target when there is HW demand. My boiler is set to a 70C max and that's as far as it will get to, even when the OT is telling it to go to 90C. This seems to be enough to recharge my unvented cylinder.

          Comment

          • HenGus
            Automated Home Legend
            • May 2014
            • 1001

            #20
            Forgetting about Evohome for the moment, how then does a condensing boiler work with a 'S' plan system? Presumably, they all have to have some form of HW priority built into them.

            Comment

            • bruce_miranda
              Automated Home Legend
              • Jul 2014
              • 2307

              #21
              Originally posted by HenGus View Post
              Forgetting about Evohome for the moment, how then does a condensing boiler work with a 'S' plan system? Presumably, they all have to have some form of HW priority built into them.
              Most boiler can probably deal with HW priority but they need to be wired and controlled with all the stuff that allows that. My isn't. So prior to the OT bridge, the boiler just fired up and reached maximum flow temperature as set on the boiler. The motorised valves just decided where to send that heated water. So when there was CH requirements, the HW recharge time in the cylinder would suffer. Add evohome and the OT bridge and the S plan still works exactly the same, except that when there is HW demand the OT bridge runs the boiler at max but when there is CH only demand then it tries to run the boiler at the lowest setting needed to fulfil all the CH demand.

              Comment

              • HenGus
                Automated Home Legend
                • May 2014
                • 1001

                #22
                I am now in contact with an 'Ecotechnician/Heating Engineer'. Further research with answers from those who seem to know is that Evohome/Opentherm works well with Atag boilers (bridge + Ebus adapter); Viessmann 100 (plus HW junction box and bridge) and Intergas (but only single zone). Intergas are looking into the problem but any solution may well require a PCB replacement. At this point, I am really beginning to wonder whether the expense of an open therm connection is actually worth the investment? I await my Ecotechnician's quote with interest.

                Comment

                • sznichol
                  Automated Home Lurker
                  • Mar 2016
                  • 4

                  #23
                  I have just had a Evohome installed to my system and have a question re settings required on the boiler PCB. I have Vaillant ecotec plus 630, previosuly with a Vaillant VRC61 wiring centre. The installer followed the following instructions,I got from previous posts on here, to get the VR33 module installed. It all seems to be working, albeit still in learning mode - seeing high boiler temp demands.

                  1.install vr33
                  2.connect x32 to x31
                  3.connect cable that was connected to x31 to the other connector on the vr33
                  4.disconnect 230v control
                  5.Ensure 24v RT and 230v are linked
                  6.wire the r8810 to the T0 terminals on the vr33

                  The 2 points I have a question about are 3 and 5.
                  3. There wasn't a connector attached to X31. We have assumed this was ok and just ignored this step
                  5. Ensure 24v RT is linked. On my boiler there are 3 terminals, marked 7, 8 and 9 for the 24v control. Which ones should be linked, if any? The installer linked pins 7 and 9, but D.016 shows 24V DC Heat Mode: 0 / Off - is this ok. The boiler does fire up, but will this affect anything else?

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #24
                    The vr33 allows the ebus signal to be further passed down to any module that might have been previously connected. Most installations won't have anything connected to X31.

                    It's interesting that you have linked 7 to 9. 7 8 9 are pins not used in the UK but are for the analogue non ebus controls. By connecting pin 7 to 9 you are effectively telling the boiler flame to be off.

                    Are you certain that the boiler is firing via the OT bridge? In which case you may just have told me why I couldn't get my boiler to fire via OT. My Vaillant 430 too didn't have the 24V RT connection. I without linking pins 7 to 9, if I just linked pins 3 and 4 (230v) then my boiler would constantly fire as though it was being fired via an external control. So if you would please confirm if your boiler is indeed firing up via the OT then that would be great. Pressing the button on the OT bridge should fire the boiler up.

                    Others with the 24V RT should be able to confirm what they see on the D.16 menu.

                    Comment

                    • sznichol
                      Automated Home Lurker
                      • Mar 2016
                      • 4

                      #25
                      I can confirm that if I press the button on the OT bridge the boiler does fire up. I am seeing a demand for 90 degrees whenever ch or dhw is required, but hopefully still in learning mode as only been installed for 1 day. When no demand then boiler switches off.

                      Comment

                      • bruce_miranda
                        Automated Home Legend
                        • Jul 2014
                        • 2307

                        #26
                        Excellent, i will put this jumper between 7 and 9 and report back. I have seen various requested flow temperatures between 46 and 90, so would be good to compare.
                        If the others can say what value they see in D.16 that would be good too, because at the moment its set to flame off.

                        Vaillant 7-8-9 terminal is a potentiometer that gradually changes the voltage from about 11V (off) to 21V DC (full throttle) to regulate heating. The 240V connector are on pins 3 and 4; they are normally bridged with a wire, which means that this 3-4 “switch” is always on, and heating may be controlled through a room thermostat on 7-8-9. However, if you disconnect the room thermostat (i.e., all 7-8-9 wires are in the air, which means ON), the heating is controlled only through 3-4. And that is what I was missing.
                        Last edited by bruce_miranda; 26 October 2016, 03:08 PM.

                        Comment

                        • StuartG
                          Automated Home Jr Member
                          • Mar 2015
                          • 45

                          #27
                          When I installed the module on my boiler I removed the existing 230V connection that was wired to the BDR91. I connected the VR33 to the expansion board on the side (for me, X31). I also had to reinstate a jumper on the 24V RT connection (for me this was X100, coloured white, and labelled RT24).

                          D.016 on mine says "controller 24v dc: heating mode 1n" if that helps!

                          Comment

                          • sznichol
                            Automated Home Lurker
                            • Mar 2016
                            • 4

                            #28
                            StuartG, we do not gave the 24v RT connection, instead we have 3 pins 7,8 and 9 where the burner off and 24v RT are on the newer boards. I have a Ecotec pro 630 which is about 7 years old.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #29
                              @sznichol if your boiler is firing up then I wouldn't worry. But because you jumped between 7 and 9 you get D.16 as 0. If you jump between 7 and 8 you will get D.16 as 1.
                              I don't know if you should do that or not. I'm going to try both and see if there is any difference.

                              Comment

                              • HenGus
                                Automated Home Legend
                                • May 2014
                                • 1001

                                #30
                                I have at last found an ecotechnician that is keen to work with me to provide an Opentherm solution with an Atag boiler. That said, I am struggling with a couple of things which are the costs/benefits of a £250 additional cost for an EBus to Opentherm converter and Opentherm bridge, and getting confirmation that the Atag Opentherm connection can cope with multiple HR92 zones? FWiW, I finally got confirmation from the guys at Intergas that their boilers do have an issue which is under investigation in The Netherlands.

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