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Thread: Loss of heat demand and binding

  1. #1
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    Default Loss of heat demand and binding

    OK just had a strange one, and this sounds very similar to what was reported on here in the last few days. (Can't pin down the specific thread unfortunately so starting a new thread)

    I noticed tonight that the living room was struggling to maintain the room temperature after the other downstairs zones had gone off - it was nearly 1C below its set point and the radiator only luke warm, which is unusual as the living room does a great job of maintaining a steady temperature.

    I didn't think too much about it as it was soon 11pm so the zone went to the night time set back of 5C. Some time later when I was preparing for bed I came into the living room to check everything was off and could still hear the gentle hiss of the radiator, despite the control panel saying it was now scheduled to 5C. Hrm...

    I checked the set point directly on the HR92 and sure enough it still said 21C when it should have been 5C at least half an hour ago. I checked on the controller on the heat demand screen and it said 14% demand from the Living room. I then turned the HR92 itself down to 5C manually and waited for that to complete. The heat demand stubbornly remained at 14% and the boiler kept going. Hrm x 2.

    I have had occasional issues before with HR92's failing to report heat demand changes to the controller so I rebooted the HR92 and tested again - still no change in heat demand with it remaining stuck at 14% regardless of turning the HR92 up or down.

    I then tried a reboot of the controller, which also didn't help. It was at this point that I noticed for the first time that the HR92 said "Unbound" instead of the zone name. Huh ?

    Unfortunately because I have the screen taped flat on that HR92 to avoid toddler damage it's difficult to see the unbound word at the bottom unless I get down at floor level, so I don't know if it was reporting unbound all along or whether it lost the binding after the HR92 and/or controller was rebooted.

    But it seems very likely that the binding was lost right at the beginning when the problem first occurred, before I intervened and was the original cause of the set point not changing and heat demand no longer propagating to the controller.

    I've never had an HR92 lose its binding status and revert to "unbound" before so that's a new one on me...

    After rebinding both the HR92 and DTS92 in the zone everything seems OK again but it's a bit unsettling that the binding mysteriously disappeared.
    Last edited by DBMandrake; 4th December 2018 at 02:24 AM.

  2. #2
    Automated Home Legend paulockenden's Avatar
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    The set-point for the zone should be coming from the DT92, shouldn't it? Stikes me that that's probably the source of the problem, rather than the HR92. If the HR92 thinks the set point is 21 then demanding 14% was probably the right thing to do.

    In your original 'reboot' phase of investigation did you also try rebooting the wall stat?

    P.

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    Quote Originally Posted by paulockenden View Post
    The set-point for the zone should be coming from the DT92, shouldn't it? Stikes me that that's probably the source of the problem, rather than the HR92.
    Ultimately its the set point at the HR92 that matters, because it's the HR92 that makes the call for heat. Changing the set point at the controller just sends a (delayed) set point change to the HR92. Changing the set point at the DTS92 sends the set point change immediately to the controller, which again, just sends a delayed set point change to the HR92.
    If the HR92 thinks the set point is 21 then demanding 14% was probably the right thing to do.
    Yes, however I quickly noticed that even minutes after I turned the HR92 down to 5C the controller still reported a 14% heat demand from the zone - and it's the only HR92 in the zone so the only possible source of heat demand. Likewise turning it up to 25C should have given a 100% demand but it remained at 14%. That's when I realised that the heat demand was no longer being sent from HR92 to controller.

    It's probably the case that the binding was already lost at this point - I suspect 14% was simply the last heat demand just before the HR92 lost its binding, and the controller just continues to "run with" that until it hears otherwise or eventually times out. (From memory timing out takes about an hour of lost comms with an HR92)
    In your original 'reboot' phase of investigation did you also try rebooting the wall stat?
    I did, but I don't recall in what order I did it.

    I think it's simply a case that some time between 6pm and 10:30pm, probably towards the latter the HR92 lost its binding and stopped communicating with the controller. I probably noticed the issue before there was time for errors to be generated in the fault log as that can take hours for some kinds of problems.

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    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by DBMandrake View Post
    Yes, however I quickly noticed that even minutes after I turned the HR92 down to 5C the controller still reported a 14% heat demand from the zone
    But CAN you turn down an HR92 in a zone with an external sensor? I didn't think you could. I thought you could only control the zone setpoint from the sensor?

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    Quote Originally Posted by paulockenden View Post
    But CAN you turn down an HR92 in a zone with an external sensor? I didn't think you could. I thought you could only control the zone setpoint from the sensor?
    You can definitely adjust the zone set point directly from an HR92 in a zone with a remote sensor - I do it all the time. It's my preferred method sometimes as it's the only way to do it without the transmission delay from the controller to HR92. For example if I'm turning up the bathroom radiator for a warm towel just before going into the shower, if I do it from the controller the shower will be half over before the set point is even applied!

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