Can't get one zone to heat up

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  • therealfronty
    Automated Home Guru
    • May 2021
    • 140

    Can't get one zone to heat up

    Hi, I've had evohome hr92 trvs on most of my radiators for about a week now, on the whole it's been working well except I just can't get my daughters bedroom to warm up fully, even if I have her target temp set to 35 degrees the system status on the controller only shows 17% demand for her zone and the valve position on the trv itself is 58%. The rad does warm up but it doesn't get as hot as it would do if I take the head off and manually open the valve

    I dont understand why the demand and/or valve position doesn't go to 100% when the room is only measuring 20 degrees with a target of 35. I've tried deleting the zone and re-adding it, even tried a completely different hr92 but for some reason I just can't get that radiator to run at full chat.

    By the way, I'm not using opentherm, the boiler is still being controlled by the old controller, so although the demand may only show 17%, this doesn't have any bearing on boiler output.

    Anyone got any ideas?
    Last edited by therealfronty; 18 May 2021, 09:45 PM.
  • Billywizzo
    Automated Home Jr Member
    • Nov 2020
    • 48

    #2
    When you refit the HR92, you do make sure you turn the black part of the body fully open for the HR92 to recalibrate.
    Have you tried swapping the HR92 with another one to see if the problem moves to the other room.

    Comment

    • G4RHL
      Automated Home Legend
      • Jan 2015
      • 1580

      #3
      Originally posted by Billywizzo View Post
      When you refit the HR92, you do make sure you turn the black part of the body fully open for the HR92 to recalibrate.
      Have you tried swapping the HR92 with another one to see if the problem moves to the other room.
      I had something similar when a room was decorated and the decorator caught the HR92 on a radiator. It showed the temperature in the room at 35c as did the Panel. It wasn't of course. I tried to override it but it reverted back to this. I resolved it by taking the batteries out of the HR92 for a few minutes, then put them back and fitted the HR92 after first fully opening the valve. Problem went.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #4
        If you have the latest firmware, it could be the Load Scaling that is causing this.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #5
          Originally posted by bruce_miranda View Post
          If you have the latest firmware, it could be the Load Scaling that is causing this.
          Indeed. If load scaling is on "Normal" try changing it to "Partial", or even off.

          Comment

          • therealfronty
            Automated Home Guru
            • May 2021
            • 140

            #6
            Not sure what load scaling is, I've got firmware 02.00.19.33 and have disabled both cold start/warm boost or whatever it's called straight away as didn't want any clever nonsense going on.

            Anyway, there is something weird going on, when the hr92 shows valve position 58%, if I take the head off I can't actually manually open the valve any more, it is already fully open, so it seems the head is reaching the 100% open point maybe earlier than its expecting (although not sure why it doesn't report 100% in that case)? So I was just having a play, and if I set valve stroke to 1, it then reports the valve position as 100% (when fully open), and also sends that back to the controller, I can see the demand for that zone goes up to 100%.

            When demand is 0, it does fully close the valve regardless of whether I set the valve stroke to 1 or 0, but it seems that on 0 it's not reporting the valve as fully open even though it is. The valve body is a TRV4 and most of my other rads are fitted with these and don't have any problems reporting the fully open valve position, so not sure why this one is different. Have left valve stroke set to 1 for now so at least in system summary I can see 100% when fully open. I need to check the temps in that room again as there might be something else going on if the valve was fully open anyway. All very odd.

            Comment

            • ally153
              Automated Home Jr Member
              • Nov 2014
              • 30

              #7
              I was about to suggest changing the 'stroke' parameter, but looks like you got there already .

              19.33 has the load scaling feature, but it isn't enabled by default, so I don't think that would be a factor - the summary screen would still show 100% from the zone anyway, when appropriate, it's just the boiler demand value which may be reduced.

              Comment

              • Billywizzo
                Automated Home Jr Member
                • Nov 2020
                • 48

                #8
                Just asking what you mean by boiler is controlled by the old controller.
                Have you removed the HR92 valve body off the rad and made sure the black part is moving freely and the pin on the rad valve is freely moving in and out.
                I had a problem where the rad would not shut so was always getting hot when other rads demanded heat and it was the HR92 valve body playing up, it was too stiff for the HR92 to turn it fully shut so had to order a new one.
                Maybe try swapping the HR92 valve body with another room and see if the problem moves rooms.
                When you refit the HR92 head, you are making sure the valve body is fully open as it recalibrates each time it is removed/refitted

                Comment

                • therealfronty
                  Automated Home Guru
                  • May 2021
                  • 140

                  #9
                  Old room stat in the living room is still wired into boiler so that is the only thing that can actually call for heat, but hr92's successfully turn off the rads upstairs during the day (and the conservatory) so all good.

                  So whether system status on the evohome controller shows 50% or 100% demand it doesn't affect boiler output as the evohome isn't connected to the boiler, and I don't have the opentherm bridge anyway so even if it was connected via a bdr91 all it could do is turn it on or off. Not sure how much % needs to show on the system status before it actually turns the boiler on, anyone know? Is there a threshold it has to go over? ie if all zones show 0, but one zone goes to 20%, is that enough to fire the boiler?

                  I've already tried swapping with another hr92 and checked the adaptor moves freely and made sure the valve is fully open when refitting.

                  It's just a bit of a mystery that the valve position on the hr92 display was only showing 58% even though the valve was fully open. Not to worry, setting it to full stroke seems to have fixed it even if it's just a display issue.

                  Comment

                  • Billywizzo
                    Automated Home Jr Member
                    • Nov 2020
                    • 48

                    #10
                    As you are not controlling the boiler via evohome, I would make sure that there is a bypass in your heating system so if the room stat fires up the boiler but none of the valves are open, the Central heating water has a circuit to flow back to the boiler. Mine is the towel rail in the bathroom.
                    It should be easy to wire in a BR91 to control the boiler and that should have been in with the evohome package.
                    Opentherm is a different wireless controller to the BR91 and only good if you have a boiler that is opentherm compatible but I believe all that opentherm does is try and make sure the boiler is in condensing mode more often by trying to ensure the water temp is in the condensing range but I am sure someone will correct me if I am wrong
                    Glad setting the valve to full stroke has sorted the issue.

                    Comment

                    • DBMandrake
                      Automated Home Legend
                      • Sep 2014
                      • 2361

                      #11
                      Originally posted by therealfronty View Post
                      Anyway, there is something weird going on, when the hr92 shows valve position 58%, if I take the head off I can't actually manually open the valve any more, it is already fully open, so it seems the head is reaching the 100% open point maybe earlier than its expecting (although not sure why it doesn't report 100% in that case)? So I was just having a play, and if I set valve stroke to 1, it then reports the valve position as 100% (when fully open), and also sends that back to the controller, I can see the demand for that zone goes up to 100%.

                      When demand is 0, it does fully close the valve regardless of whether I set the valve stroke to 1 or 0, but it seems that on 0 it's not reporting the valve as fully open even though it is. The valve body is a TRV4 and most of my other rads are fitted with these and don't have any problems reporting the fully open valve position, so not sure why this one is different. Have left valve stroke set to 1 for now so at least in system summary I can see 100% when fully open. I need to check the temps in that room again as there might be something else going on if the valve was fully open anyway. All very odd.
                      Originally posted by therealfronty View Post
                      Old room stat in the living room is still wired into boiler so that is the only thing that can actually call for heat, but hr92's successfully turn off the rads upstairs during the day (and the conservatory) so all good.

                      So whether system status on the evohome controller shows 50% or 100% demand it doesn't affect boiler output as the evohome isn't connected to the boiler, and I don't have the opentherm bridge anyway so even if it was connected via a bdr91 all it could do is turn it on or off. Not sure how much % needs to show on the system status before it actually turns the boiler on, anyone know? Is there a threshold it has to go over? ie if all zones show 0, but one zone goes to 20%, is that enough to fire the boiler?

                      I've already tried swapping with another hr92 and checked the adaptor moves freely and made sure the valve is fully open when refitting.

                      It's just a bit of a mystery that the valve position on the hr92 display was only showing 58% even though the valve was fully open. Not to worry, setting it to full stroke seems to have fixed it even if it's just a display issue.
                      Why are you still using the old room stat to control the boiler instead of Evohome?

                      Evohome's algorithms are designed to control heat output of radiators by controlling both the individual water flow through each radiator and by controlling the duty cycle of the boiler, which is derived from the heat demands sent from the individual HR92's in each zone.

                      The configuration you have is unsupported and you should not expect the system to work properly in this state. Unless you have a good reason not to I'd strongly suggest you ditch the original wall stat and give Evohome control of the boiler, otherwise you can't expect it to work properly.

                      As for the stroke setting - it sounds like your valve bodies are very stiff either by design (not fully compatible with the HR92 from day one, even if they screw on OK) or have become stiff with age (perished rubber washer inside or rusting slide pin inside) and if one radiator needs stroke 1 and all the other radiators use the same valve body design I would recommend setting all HR92's to stroke 1 mode. (I use stroke 1 mode on all my radiators and found I needed to)

                      If you do, make sure after changing the setting that you remove each HR92, turn the black wheel anti-clockwise then refit it - this will trigger a valve pin calibration with the new stroke setting so that it can calibrate the fully closed and open positions.

                      Regarding heat demands - if you use a BDR91 relay any heat demand over 10% as reported in the system settings page will bring the boiler on, assuming you have load scaling disabled, which is the default. Keep in mind that if you use a relay it's not just full on or full off, it uses TPI - a form of duty cycle modulation so the boiler is switched on for a certain percentage of each cycle period. (default cycle time is 10 minutes) So the higher the heat demand the greater proportion of each 10 minute period the boiler is on, giving a form of proportional control.

                      If you use Opentherm I believe any heat demand 1% and above will bring on the boiler and the requested flow temperature is proportional to the heat demand. The flame in the boiler may of course shut off if the requested flow temperature is already reached, leaving just the pump circulating.
                      Last edited by DBMandrake; 21 May 2021, 09:05 AM.

                      Comment

                      • therealfronty
                        Automated Home Guru
                        • May 2021
                        • 140

                        #12
                        Lots of interesting discussion points! :-)

                        Currently I have two rads in the living room where the old wall mounted roomstat is, neither currently has a TRV (as you'd expect). The roomstat is still controlling the boiler simply because I haven't gotten around to wiring in the boiler relay yet (I have got one, it's just plugged into a mains socket so I can see the green light come on and off, although nothing is wired into the relay contacts yet - I'm going to reposition it temporarily in the airing cupboard to check the wifi signal is good before wiring it in properly). What I'm intending to do is fit hr92s to these two rads, but I'll have to change the old valves to fit TRVs. That means a drain down (system is due a flush, clean and inhibitor anyway) plus I have a third rad that has an incompatible TRV body so will change that at the same time. My rad in the bathroom doesn't have a TRV so that will become my bypass, I don't have a ABV on this system but it is open-vented, so I was wondering wouldn't the pump just pump water out of the expansion/overflow pipe into the header tank if every radiator was closed? I'll have the bathroom rad acting as a bypass anyway.

                        As for replacing the roomstat, that is hard wired into the wall, so what I intend to do is disconnect the roomstat wire in the wiring centre and replace it with the BDR91, then use the roomstat wire to feed DC to the controller, so I need to get a wall mount kit and wire the transformer into the mains up by the wiring centre. Obvs can still use the evotouch in the living room just using it's tabletop mount for now.

                        I have a Viessman 100 open vent boiler (which is opentherm compatible) on a y-plan, so the current controller is controlling the pump, 3 port valve, DHW etc. The heating is set on constant already as the roomstat has a timer (to be replaced by Evohome), so the old controller will just control the DHW on a timer, however I do also have the hot water kit so could add that too, but looking at all the wiring I think I'll need to get someone in for that unless I can trace all the wires and figure out what they all do, then use a new wiring centre (I've seen the honeywell one in screwfix that is basically a giant 10 way chocolate block). So hopefully I can then get rid of the old controller and tidy up some of the wiring.

                        Good to know about TPI, tbh my Mum has opentherm on her boiler and it does seem that when it's close to the set point the rads don't get very warm and it spends hours with the pump running and firing for short periods - I'd rather it just warm the rads up, dump some heat then shut off, but I know it's all about preventing undershoot/overshoot etc. So if I fit the opentherm bridge it's probably the last thing I'll do.

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #13
                          Originally posted by therealfronty View Post
                          Lots of interesting discussion points! :-)

                          Currently I have two rads in the living room where the old wall mounted roomstat is, neither currently has a TRV (as you'd expect). The roomstat is still controlling the boiler simply because I haven't gotten around to wiring in the boiler relay yet (I have got one, it's just plugged into a mains socket so I can see the green light come on and off, although nothing is wired into the relay contacts yet - I'm going to reposition it temporarily in the airing cupboard to check the wifi signal is good before wiring it in properly). What I'm intending to do is fit hr92s to these two rads, but I'll have to change the old valves to fit TRVs. That means a drain down (system is due a flush, clean and inhibitor anyway) plus I have a third rad that has an incompatible TRV body so will change that at the same time.
                          Sounds like a plan. Before I had Evohome my bypass radiator was the hall way so I had to add a TRV valve body to that one to get HR92's on all radiators, and also added an automatic bypass valve.
                          My rad in the bathroom doesn't have a TRV so that will become my bypass, I don't have a ABV on this system but it is open-vented, so I was wondering wouldn't the pump just pump water out of the expansion/overflow pipe into the header tank if every radiator was closed? I'll have the bathroom rad acting as a bypass anyway.
                          You definitely don't want the system to be "pumping over" through the header tank as that will oxygenate the water leading to both air bubbles in the system and corrosion in the radiators...

                          If there's too much differential pressure in an open vented system (my system is open vented as well) it can cause air to be sucked into the system from the vent pipe, especially during a pump shutdown/start-up transient. (You might hear a gurgling noise)

                          Whether it pumps over or sucks in air due to low pressure depends on where the pump is connected in relation to the boiler and vent lines, and not all vented systems have the pipes in the correct configuration.

                          See here for some details about both these problems:

                          Diy heating plumbing tips 6 looks at the installation issues regarding circulators in a fully pumped central heating system.


                          In short, no you can't rely on pumping over to get away without an automatic bypass valve on a system with all radiators controlled. If you want to control all radiators (as I do) then you need an automatic bypass valve especially on an open vented system where there is risk of pumping over or sucking in air due to pressure differentials.

                          As for replacing the roomstat, that is hard wired into the wall, so what I intend to do is disconnect the roomstat wire in the wiring centre and replace it with the BDR91, then use the roomstat wire to feed DC to the controller, so I need to get a wall mount kit and wire the transformer into the mains up by the wiring centre. Obvs can still use the evotouch in the living room just using it's tabletop mount for now.
                          This is exactly what I did - removed the old hard wired wall stat, installed the BDR91(s) in the boiler closet connected directly to the wiring centre, installed the wall mount transformer inside the wiring centre box and re-purposed the wire run to the wall mount for 5v - not installing the transformer behind the wall mount also allowed me to flush mount the wall mount without a back box where the wire comes through the wall which saved me carving out a lot of brick and plaster...

                          The only thing to watch out for is voltage drop across a long cable run at the low 5 volts the device operates at - if you have full size 16amp mains flex like mine did you'll be OK, but if the old thermostat was connected via thinner wire you might have an issue. For some inexplicable reason the voltage from the transformer in the wall mount is lower than the table top stand as well - the table top stand puts out 5v while the wall mount is only about 4.6v. (!)
                          Last edited by DBMandrake; 25 May 2021, 03:25 PM.

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