Evohome Opentherm - tearing my hair out!

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  • billytkid
    Automated Home Jr Member
    • Mar 2018
    • 29

    Evohome Opentherm - tearing my hair out!

    Hi all,

    after taking the plunge of first evohome and then deciding to go upgrade it to opentherm I'm having no end of issues.

    I've got a Vallient boiler using a VR33 module and this interfaces fine with the Evohome opentherm interface - pressing the button switches between 90Deg and 10 Deg draw whichi I can monitor on the boiler.

    However, I could hear the boiler firing a lot even though there was 0% requirement from the zones so I put a temp logger on the flow/return on the boiler, and I was right, throughout the night the boiler is pushing out between 40>60 Deg, despite only one zone being set at 17.5D needing a slight amount to keep it's temp, and certainly not all night needing a draw at these temps.

    I tested the theory and have attached a photo of 0% draw, yet the boiler seeing Ebus target value of 56Deg.20180427_215355.jpg20180427_215335.jpg.

    The signal from the controller to the boiler is perfect (5 flashing red dots).

    In addition to this I've also seen another weird bug, where the kitchen being at 21.5Deg, setpoint at 10Deg, yet it saying it needs 10% pull from the boiler, see below:
    20180428_131618.jpg20180428_131603.jpg

    I love the idea of this system, but at the moment it's seriously failing WAF and is buring way too much gas.

    Are there any hidden screens (beyond the hold setting button for 3 seconds) where I can see more details about what is pulling/sending info where?

    HELP!!

    thanks
  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #2
    Do you have any other eBUS controls on the boiler itself?

    Comment

    • billytkid
      Automated Home Jr Member
      • Mar 2018
      • 29

      #3
      Originally posted by bruce_miranda View Post
      Do you have any other eBUS controls on the boiler itself?
      Nope just the vr33 to the evohome.

      Comment

      • DBMandrake
        Automated Home Legend
        • Sep 2014
        • 2361

        #4
        Had you just rebooted the controller before you took those last two pictures ? Because an hourglass means it hasn't received a temperature measurement from a zone since rebooting, or hasn't received a measurement in over an hour, the latter suggesting a wireless comms problems.

        Also the controller showing a 0% heat demand for opentherm but the boiler showing a requested temperature of 56C indicates a comms problem. What you are showing is not the way the system should be working so you need to start following the procedures to troubleshoot wireless comms issues.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #5
          I have a 438, which is an extremely old boiler and the VR33 and OT work well. I am not saying the OT implementation is good but it works. Also you said your kitchen had a set point of 10C but the picture shows 20C. Note the controller rounds up the actual temperature so the 21.5 could easily be a rounded figure and close enough to the set point of 20C for a low Heat Demand.

          Comment

          • matjholden@yahoo.co.uk
            Automated Home Jr Member
            • Oct 2017
            • 11

            #6
            What boiler do you have? I have the same issue with my ecotec pro 28.( demand for heat even when everything is showing 0%). I have taken to limiting the boiler to 55 degrees to reduce the impact.

            I did suspect a comms error but I tried moving the controller next to the opentherm receiver and the problem persisted. I also tried moving the receiver and no change. I only have the problem when one of the zones is within a degree of the set point. I put this down to being by design.

            My main issue was that it seems to ask for a higher temperature, sometimes 75 degrees when at 0%. When a small percentage is being asked for this can be as low as 47.

            Comment

            • billytkid
              Automated Home Jr Member
              • Mar 2018
              • 29

              #7
              Morning

              Looking at the temp reading this morning I've had another night of Opentherm calling for 40>50 degrees all night, despite all zones being off.
              chart.jpg

              @DBMandrake - yes I'd just rebooted (seeing if that'd fix it), however I took the photos to show how it was before and after the reboot.

              @bruce_miranda - Thanks, however I don't see how an actual temp of 21.5 and a setpoint of 20 should cause any form of draw. 1.5D overshoot and then continuing to call for heat is weird.

              @matjholden - Vallient Ecotec pro 630.

              I'm tempted of deleting everything and doing a full reset, can anyone think of any other options?

              thanks

              Comment

              • billytkid
                Automated Home Jr Member
                • Mar 2018
                • 29

                #8
                I did just try again a signal test and all looks fine, however one thing which it'd be good for other to check.
                When checking DHW both Opentherm module and BDR91 flash 5 times (full signal), and likewise when checking boiler CH call both again flash.

                Is this what you guys see?

                Also, here is a bit more data on last night. At the bottom is the only room in the house calling for heat, so I can see why the boiler comes on, but what the hell is the massive varience in pull temp for a 17.5deg setpoint?! Surely it shoudl be calling for nearer to 30 to keep that one room constant?

                chart (1).jpg
                Last edited by billytkid; 29 April 2018, 07:37 AM.

                Comment

                • paulockenden
                  Automated Home Legend
                  • Apr 2015
                  • 1719

                  #9
                  Just trying to think of something different.... could it be an ABV that’s too slack? A zone might be calling for a tiny amount of heat because it’s in the proportional band (plus or minus 1.5 degrees), but if most of the boiler output was going round the bypass loop the zone would keep demanding more heat.

                  Comment

                  • matjholden@yahoo.co.uk
                    Automated Home Jr Member
                    • Oct 2017
                    • 11

                    #10
                    What I have noticed is that when changing from a 10 degree demand the opentherm always requests a 90 degree demand next. This isn't an issue when a number of radiators are demanding heat as after a minute or two the demand is updated to something more suitable but when only one radiator is demanding heat or the opentherm is demanding heat with all the radiators at 0% it causes high flow temperatures hence my decision to set the max ch temp to 55.

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #11
                      Evohome will always call for 100% unless all zones are within the proportional band (I.e within 1.5 degrees of the set-point).

                      Comment

                      • billytkid
                        Automated Home Jr Member
                        • Mar 2018
                        • 29

                        #12
                        There is only the one zone during these hours calling for heat and it's at the setpoint, and keeping there.

                        I don't understand however as this is they case why is there such massive variances in flow rates every 5 mins, I thought the point of Opentherm is that if it wants 30deg, it pulls it?

                        Could it be I've set my vallient partial load to be 35kw? This still wouldnt explain the call for heat when none needed, but may explain the highs/lows frequency?

                        thx

                        Comment

                        • paulockenden
                          Automated Home Legend
                          • Apr 2015
                          • 1719

                          #13
                          None needed? If the zone is at setpoint there IS a demand needed to keep it there, else it would cool down. That's one of the fundamental things about how Evohome works.

                          Are you saying that you're artificially configured your boiler so that it can’t fully modulate down to a low output?

                          Comment

                          • billytkid
                            Automated Home Jr Member
                            • Mar 2018
                            • 29

                            #14
                            Hi Paul,
                            as per my first post in this chain the boiler is showing a demand when Evohome says there isn't one, this may be explained however by the 1.5+/- you've said where it may pull.

                            However the point of opentherm is that it shoudl say 'give me 30 degrees flow' and the boiler will do that, however the graph shows that the boiler output is modulating at 60 degrees every 5 mins, which negates the whole point of opentherm, I might as well go back to the BDR91 and let my boiler work out what do do.

                            On the valient you can set max flow rate (currently 70deg) and partial load output, either auto, or anything between 10kw >

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #15
                              The way a Vaillant boiler works is that any partial load set is the max the boiler can modulate to. However the boiler will modulate below this number. Most newer Vaillant have an Auto range rate setting, why not use that? My 438 boiler doesn't have that.
                              With the current implementation of OT any set point that is within 1.5C of the temp will cause a Heat Demand. And any temperature that is lower than 1.5C of the Set point will cause maximum demand.
                              The only bit I cannot explain without some data on your system is why when there is 0% Heat Demand from everything the boiler is still firing. Are you sure the boilers pump over run time is not bridging two actual brief demands thus making the boiler appear on all the time? Do you have any means of capturing the real time heat demand and boiler target temperatures?

                              Comment

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