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Thread: Can't get one zone to heat up

  1. #1
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    Question 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; 18th May 2021 at 10:45 PM.

  2. #2
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    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.

  3. #3
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    Quote 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.

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

  5. #5
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    Quote 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.

  6. #6
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    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.

  7. #7
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    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.

  8. #8
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    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

  9. #9
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    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.

  10. #10
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    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.

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