Evohome Opentherm - tearing my hair out!

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  • billytkid
    Automated Home Jr Member
    • Mar 2018
    • 29

    #16
    Originally posted by bruce_miranda View Post
    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?
    Ok, I get the first bit, however should evohome be asking for say 40 degrees and the boiler giving that? I don't see how I'm getting burst of 60 degrees requested + delivered with opentherm. The required flow temp should be much lower and only high 60+ when at max (ie DHW demand or when rads need more than 1.5deg from their setpoint).

    On the second point I can see on the boiler that the opentherm is calling for heat, rather than it just being the overrun. Sadly I cant see in realtime the head demand call, other than be keeping my head in the cupboard.

    Could resetting the system possibly solve this? Although I'd be annoyed as I'd lose the historical data in Domoticz.

    Finally, I've raised a ticket with Honeywell, can they see more diagnostic info that we can?

    Comment

    • bruce_miranda
      Automated Home Legend
      • Jul 2014
      • 2307

      #17
      Yes Honeywell can see more data if you give them permission to suck that from your controller. Sadly the Heat Demand isnt on the app app, but atleast it's visible these days.
      Try this. For a 2 hour period make ALL your setpoints for every zone low, much lower that 3C from the room temperature but higher than the 5C OFF. Then within that time keep an eye on the Heat Demand screen, I think it updates and will show you refreshed values. Check if you have the boiler fire with a confirmed 0 Heat Demand. For me that is your issue.
      If you boiler flow is ramping up beyond the Target flow set in D.9 then you have a different issue.

      Comment

      • mtmcgavock
        Automated Home Legend
        • Mar 2017
        • 507

        #18
        Do you ever have a period where the boiler shows no demand? (as in the little radiator goes off the screen on the boiler).

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #19
          Originally posted by billytkid View Post
          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?
          Yes, on a stored hot water system it seems to be normal for all the Relay lights to flash no matter whether you choose to test hot water or heating.

          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?

          [ATTACH=CONFIG]1264[/ATTACH]
          That may be a sign that that particular zone suffers from overshooting and oscillation - if you're able to graph the heat demand from the HR92 (Domoticz with an HGI80) you'll probably find that it is oscillating up and down. Also check the measured temperature for a 1-2C oscillation in temperature.

          When only a single zone is calling for heat, the requested Opentherm temperature is more or less dictated by the call for heat of that one HR92. If for some reason it is struggling to keep the temperature steady and ends up opening and closing a lot, this will naturally cause the call for heat to go up and down and so the flow temperature request.

          This will not tend to happen when there are multiple zones calling for heat at the same time because the call for heat is dictated by the zone with the highest demand, so any oscillation of lower demand zones won't have much effect on the heat demand sent to the boiler.

          Something that may cause an unusually high heat demand from the boiler from a single zone at 17C, is if the valve is not calibrating the valve body properly. If you check the valve position (option 10 in the HR92 menu) it goes from 0 to 100 with 0 representing the pin pushed fully down and 100 fully up.

          Ideally the valve should just start allowing water to flow at a pin travel of 30. This is also the point where the HR92 starts calling for heat from the boiler.

          If due to a sticky or incompatible valve body the water doesn't start to flow until say 40 or 50% pin travel, it will actually be calling for heat from the boiler before the valve opens enough to allow water flow through the radiator. Which means by the time it finds the point where the valve opens and it can maintain the room temperature correctly (which your graph shows is happening) the flow temperature will be unnecessarily high.

          You could try forcing the HR92 in that zone to recalibrate - remove it from the radiator, turn the black wheel full anti-clockwise (open) and then refit the HR92. After about a minute it will say cycle.

          Whenever fitting or refitting HR92's you should always fully wind the black wheel anti-clockwise to allow it to calibrate properly.
          Last edited by DBMandrake; 29 April 2018, 06:06 PM.

          Comment

          • billytkid
            Automated Home Jr Member
            • Mar 2018
            • 29

            #20
            Thanks DBMandrake,

            I've reset the head to see if this'll solve it, but the graph below shows flow/return, and this one zone in particular which tracks it setpoint almost exactly.

            chart.jpg

            I'll wait for Honeywell to look at the back end data to get their heads around it, and in the meantime I'll set the boiler partial load to be auto (although i only put this on max from other posts saying to handovre all control to opentherm).

            thx

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #21
              Because of the compressed scale it's hard to tell, but it looks to me like the temperature is tracking the setpoint quite well?

              P.

              Comment

              • billytkid
                Automated Home Jr Member
                • Mar 2018
                • 29

                #22
                Originally posted by paulockenden View Post
                Because of the compressed scale it's hard to tell, but it looks to me like the temperature is tracking the setpoint quite well?

                P.
                Yes, exactly, so why is Evohome calling for 60degrees to do this evey 5 minutes? why not a 30degree constant call to take advantage of the condensing boiler?

                If it tracks well, but only does this from MAX to off, then what's the point with opentherm? Might as well go back to the BDR91..

                Comment

                • paulockenden
                  Automated Home Legend
                  • Apr 2015
                  • 1719

                  #23
                  But do you know that Evohome is definitely calling for 60 degrees? Could it be that with your boiler modulated down to its lowest power and with slow pump speeds then it can’t go any lower than 60 degrees? Or could it be one of those boilers that, when asked for a low demand, start off at max and then slowly ramp down (I remember someone reporting this with one particular boiler on the forums here).

                  Too many variables.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #24
                    Also didn't you say, your boiler flow was set to 70C. It appears that for most of the time the flow is hovering around the 60C mark. So the flow is operating lower than if the boiler was run off a BDR91.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #25
                      It will really help if you can track the D.9 temperatures when all of this is happening. That's the only thing the boiler cares about. It will try to match the flow to what is requested on D.9.

                      Comment

                      • HenGus
                        Automated Home Legend
                        • May 2014
                        • 1001

                        #26
                        Originally posted by billytkid View Post
                        Yes, exactly, so why is Evohome calling for 60degrees to do this evey 5 minutes? why not a 30degree constant call to take advantage of the condensing boiler?

                        If it tracks well, but only does this from MAX to off, then what's the point with opentherm? Might as well go back to the BDR91..
                        I think that you might be expecting too much of Evohome/Opentherm. I have never seen a flow temperature of 30C on my Atag boiler once the house is within its set temperature range. I think that Paul is correct. My boiler can drop from 24 to 5kWs. On start, the flow temperature slowly increases to the Set Max flow temperature of 70C. It will stay at 70C until all zones demanding heat are within their set range before falling back to about 47C depending on the outside temperature.

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #27
                          The lowest I have ever seen actually requested is 39C but more often it is about 45C. So 30C flow is not going to happen.

                          chart.jpg

                          See yesterday and this morning's demand. Now think if a BDR91 ramping up to the full 70C is better or OT. What luck I can clip my boiler to my chosen max of 65C. Yikes, imagine if I had a Viesmann and my radiators were running at 90C for that long!

                          More notably, look how between 10pm and 5am everything is quiet at the boiler. All my set points drop to 8C overnight.

                          From experience, OT works well when all zones are used. Evohome zone schedules and OT don't play particularly nicely especially if zones keep falling more than 1.5C away from their set points.
                          Last edited by bruce_miranda; 30 April 2018, 11:48 AM.

                          Comment

                          • HenGus
                            Automated Home Legend
                            • May 2014
                            • 1001

                            #28
                            Originally posted by bruce_miranda View Post

                            From experience, OT works well when all zones are used. Evohome zone schedules and OT don't play particularly nicely especially if zones keep falling more than 1.5C away from their set points.
                            I agree 100%. Maximum efficiency is achieved by getting the house up to the desired set points and leaving it there. My home is also set to 8C from 10:30pm until 7.30am and the boiler has stopped firing overnight as zones now never fall that low.

                            Looking at my usage monitor, the last hour has used 0.26CM3s of gas or about 3kWhs/10p.
                            Last edited by HenGus; 30 April 2018, 12:19 PM.

                            Comment

                            • dty
                              Automated Home Ninja
                              • Aug 2016
                              • 489

                              #29
                              Originally posted by bruce_miranda View Post
                              The lowest I have ever seen actually requested is 39C but more often it is about 45C. So 30C flow is not going to happen.
                              I had a period of about 20 minutes on Friday 20th where mine was calling for 26C.

                              Comment

                              • billytkid
                                Automated Home Jr Member
                                • Mar 2018
                                • 29

                                #30
                                Hi all,

                                I'm getting to the bottom of this...

                                The crazy nightime high output, I think this is down to a bug in EvoHome. I use Domoticz to set actions based on my alarm system, and when going to bed it sets EvoHome into 'Custom' mode which turns off the heating downstairs, then at 1am it sets EvoHome into normal mode. It's at 1am that the crazy heat demand start. I've checked in the schedules of all devices and none of them at 1am have a setting to call for heat. Turning off the 1am reset (and indeed the going to bed custom mode) have stopped the issue.

                                This is the URL I call to set the 'normal mode' http://XXXYYY:8080/json.htm?type=com...=Auto&action=1

                                Can anyone replicate this?

                                I've also spoken to Honeywell regarding the random calls for heat and they've said this may be down to learning - but seemingly they can't see anything extra in their systems beyond what we can...which doesnt help.

                                Comment

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