Evohome + which OT Boiler?

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  • fergie
    Automated Home Sr Member
    • Mar 2017
    • 92

    Evohome + which OT Boiler?

    I'm planning to change my boiler soon and looking for recommendations for what would work best via multizoned evohome while fully utilising open therm.

    My current set up is a heat only boiler in S plan with unvented tank in cupboard with pump and expansion vessel.

    I'd be looking for aprox 30kw and can go to either reg or system boiler. Combi isn't really an option.

    Thanks.
  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #2
    Start with this http://www.wordpress-1219309-4387497...ight=opentherm

    Comment

    • fergie
      Automated Home Sr Member
      • Mar 2017
      • 92

      #3
      Looks like my options are along these lines:

      Atag iS32
      Ideal Vogue G2 32
      Ideal Logic+ Heat
      Valliant Ecotec plus +VR33

      Any thoughts?

      Comment

      • stevejclarke
        Automated Home Lurker
        • Feb 2017
        • 5

        #4
        You could add the Viessmann Vitodens 100W to that list, that's what I've just installed and am currently awaiting the arrival of the OT module, but it's working ok so far in TPI mode

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #5
          After reading the other posts regarding another Viessmann model and OT, I don't know if I'd recommend Viessmann, just yet.

          Comment

          • fergie
            Automated Home Sr Member
            • Mar 2017
            • 92

            #6
            It seems a lot of the combinations of boiler plus OT will work in theory, but no one seems to be posting examples of it actually working. Sadly it seems to be example after example of something not working properly?

            Comment

            • stevejclarke
              Automated Home Lurker
              • Feb 2017
              • 5

              #7
              Yes, I'm just beginning to catch up on the recent OT threads and will be interested to see if my 100W suffers the same problem of not being able to limit the CH flow temp when my OT bridge arrives. My rads are sized for a flow temp of 55 deg as it was intended to install a heat pump, so limiting the flow temp will be quite important. Very happy otherwise with the Viessmann so far though and the internal diverter valve and DHW controller work very nicely and simplify the plumbing and controls.

              Comment

              • fergie
                Automated Home Sr Member
                • Mar 2017
                • 92

                #8
                Good luck - I had read about issues with the Weismann.

                Can anyone actually name any system or reg boilers that work well with multizone evohome via Opentherm?

                Comment

                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #9
                  A Vaillant with the VR33 seems to do a good job. My real issue is around the implementation of OT itself and the fact that it runs the boilers at full for longer than it should - or at least I think so. Of course a lot better than running it at full all the time like in a normal thermostat scenario. But thank goodness the Vaillant doesn't suffer from the issue that the Viessmann has, about not being able to control what the max temperature was, that would have really got me going against OT.

                  Comment

                  • StephenC
                    Automated Home Guru
                    • Feb 2017
                    • 102

                    #10
                    I'd agree - ignoring the Viessmann max CH flow temp issue - my thoughts based on observations are the same as bruce_miranda, and that "max ch flow temp" is requested for too long - right up to and a little over the set point, meaning radiator sizing for heat loss is even more crucial than before. As per this thread with the trend towards fitting larger radiators in rooms to account for lower flow temps in condensing boilers and even heat pumps, this again goes against OT requesting "max temp" which could be outside condensing ranges.

                    I would think the Honeywell OT implementation as-is would be better suited to a well insulated house with very minimal changes throughout day and night, and therefore its unlikely to need to call for "max power!!". It would be in condensing mode the vast majority of the time.

                    Of course, for an older solid wall, uninstalled or poorly insulated house like many in the UK, setting the night (or even day if out at work for example) temps back can produce significant savings (as I have seen). I suspect any savings I had expected for OT will not materialize due to the lack of condensing occurring during warm up from cold phases. Its is too early to say really with any accuracy however.

                    A well designed system of interfaces should (in my opinion) have fail-safes/checks built in on both sides, in this case to "catch" a silly (I don't know - how about 90 degrees, nearly boiling???!) temp request and knock it down to something safe. There is no reason in my mind why in my case Viessmann are 100% accountable for the lack of CH flow temp control. This should also be configurable on the Evohome side seeing as that is the very point of OT - to be able to control the CH flow temp. Either interface can then be configured with a max value, and the lowest is then used. Simple, right?

                    To have neither side check (or allow) the temp for user set config creates the situation where we have it now. A right mess and finger pointing from both sides initially. That said, Honeywell are investigating this now. Viessmann are not... I estimate I have another ~8 years or so with this boiler (~10 year life assumption), so will need to figure this out or go back to BDR91 + weather comp.

                    Its a check and balance approach that seems to be needed due to clear lack of communication and understanding of how each others components in the system inter-operate.

                    Comment

                    • fergie
                      Automated Home Sr Member
                      • Mar 2017
                      • 92

                      #11
                      My house is almost 10 with decent insulation. If anything I'd say the rads are undersized, but maybe that is a good thing.

                      It's looking like my options are:
                      1. Forget OT and go intergas eco rf + wc.
                      2. Go Valliant + 33 module
                      3. Atag, but no one seems to have tried it yet - though they claim it works well.
                      4. Ideal - same as above.
                      Last edited by fergie; 23 March 2017, 03:11 PM. Reason: Info

                      Comment

                      • dty
                        Automated Home Ninja
                        • Aug 2016
                        • 489

                        #12
                        I can confirm Vaillant + VR33 works - at least for the Vaillant EcoFit Pure system boiler I've just had fitted.

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #13
                          The VR33 is simply an OT to eBUS bridge. So in theory should work with any Vaillant boiler. My 438 boiler that has needed some "off manual" tweaking but worked fine too.

                          Comment

                          • fergie
                            Automated Home Sr Member
                            • Mar 2017
                            • 92

                            #14
                            My Atag iS32 + hot water kit seems to be working very well. Though heating is now effectively off for the 'summer'.

                            Comment

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