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Thread: Evohome Multi radiator per room bug or being clever?

  1. #1
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    Default Evohome Multi radiator per room bug, being clever or something else?

    Hi

    I've been battling with my Evohome install for a while where I've two rooms both with two radiators in each, where in both cases the second radiators radiators appeared to be the only ones getting hot (unless there was a high increase in heat demand say first thing in the morning). This isn't a balancing issue as the radiators all come up to heat quickly without the HR91's attached. I also noticed in both rooms, that the 1st radiators appeared to only be opening a small amount under low heat demands (proven by removing the HR91s), whereas the 2nd radiators are both opening more, thus allowing hot water to flow. Tried changing the zone to single/multiple rooms and this had no effect. Re-created zones, reset bindings loads of times, no effect. Checked and both zones had two actuators listed, and both tested perfectly with the RF zone check.

    So in an attempt to try and workout what was going on I added each radiator to its own zone, essentially creating 4 zones (Kitchen 1, Kitchen 2, Living Room 1 and Living Room 2) with 4 radiators, initially under low load, each radiator started warming.

    So the question is.... When you add multiple radiators to a zone, does Evohome try and be clever by only using 1 radiator when the heat demand is low, say < 40%? What's odd is in both cases the 1st radiators were in cooler parts of the room (proven by them reporting a lower temp where split into 4 zones), yet it was favouring heating only the second radiators to bring the room up to temp.

    Thoughts, in both cases the rooms are quite big, so only having 1 radiator in each room heating on low load means the rooms take longer to heat, so for the moment I'm sticking with 4 separate zones.

    I've recently changed our radiator valves to Valencia, could it be that the HR91s need to re-learn opening positions, heat up speeds etc...? Or could it be that I should just leave things to settle down for a few days, maybe all my fiddling is causing the HR91 learning to be reset and not adjust?

    Dan
    Last edited by daniel@paynefamily.co.uk; 25th January 2021 at 06:46 PM.

  2. #2
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    It sounds as though something went wrong when you were binding the TRVs. If there are two radiators in a room you choose which you want to be in control and bind that first. Once done the Control Panel will let you bind the second. The first will thenceforth be the main communicator with the Panel. Way back in time I got it wrong and started again. If you still have the issue I suggest you unbind the TRVs in the relevant rooms and start afresh. A better approach is to use a free standing thermostat. In my one room in which I have 2 HR92s I use a Y87RF thermostat to manage temperature. It is far far better.

    Incidentally I can often find the temperature reading on the HR92 way off what it is. For example in one room the HR92 was reading 22C. A room thermometer at about waist height on a sideboard 6 feet away read 18C. I am in this room now as I write. My wife said she was cold. I turned the HR92 up to 24C. It now reads 24c but a separate thermometer says it’s 20c. I don’t find this in the room with the Y874Rf. I have now installed a Y87RF in my study to monitor the discrepancies further. At present it reads 17.5C, the HR92 reads 17C and two independent thermometer read 16.5C. Ideally I should install a Y874RF in every room, recommended by many in this forum, but the cost of such and the fact that my heating system will shortly be changed, means I am holding back. Generally though the HR92 does not display the real temperature of the room experienced at say shoulder or head height in a location free from draughts or other influences. The accuracy of the HR92 is I think a little suspect and clearly influenced by its proximity to the radiator. I can of course adjust for that in the settings in the HR92.

  3. #3
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    Could you please advise me of the differences between the Y87RF and the DTS92 which seems to perform a similar job?

    I have a DTS92 controlling 2 radiators in one room, and also in another room where the radiator is badly sited to allow control by its HR92.

    NJSS

  4. #4
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    Quote Originally Posted by FullBore View Post
    Could you please advise me of the differences between the Y87RF and the DTS92 which seems to perform a similar job?

    I have a DTS92 controlling 2 radiators in one room, and also in another room where the radiator is badly sited to allow control by its HR92.

    NJSS
    I can’t answer this one as I don’t have a DTS92 but am sure somebody will step in here.

  5. #5
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    Quote Originally Posted by G4RHL View Post
    I can’t answer this one as I don’t have a DTS92 but am sure somebody will step in here.
    I believe from my previous research, that The Y87RF is a more user friendly thermostat. The DTS92 (which I have 3 in my setup) is not the easiest to use as you have to press the up/down button, then wait for it to give you the current readout, then using the buttons change the temp to the desired setting. Many times the new setting doesn't "take" and I have to redo. The Y87RF didn't exist when I built my system but I do like the look of it and when any of my DTS92's break I will switch to the Y87RF

  6. #6
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    Quote Originally Posted by daniel@paynefamily.co.uk View Post
    Hi

    I've been battling with my Evohome install for a while where I've two rooms both with two radiators in each, where in both cases the second radiators radiators appeared to be the only ones getting hot (unless there was a high increase in heat demand say first thing in the morning). This isn't a balancing issue as the radiators all come up to heat quickly without the HR91's attached. I also noticed in both rooms, that the 1st radiators appeared to only be opening a small amount under low heat demands (proven by removing the HR91s), whereas the 2nd radiators are both opening more, thus allowing hot water to flow. Tried changing the zone to single/multiple rooms and this had no effect. Re-created zones, reset bindings loads of times, no effect. Checked and both zones had two actuators listed, and both tested perfectly with the RF zone check.

    So in an attempt to try and workout what was going on I added each radiator to its own zone, essentially creating 4 zones (Kitchen 1, Kitchen 2, Living Room 1 and Living Room 2) with 4 radiators, initially under low load, each radiator started warming.

    So the question is.... When you add multiple radiators to a zone, does Evohome try and be clever by only using 1 radiator when the heat demand is low, say < 40%? What's odd is in both cases the 1st radiators were in cooler parts of the room (proven by them reporting a lower temp where split into 4 zones), yet it was favouring heating only the second radiators to bring the room up to temp.

    Thoughts, in both cases the rooms are quite big, so only having 1 radiator in each room heating on low load means the rooms take longer to heat, so for the moment I'm sticking with 4 separate zones.

    I've recently changed our radiator valves to Valencia, could it be that the HR91s need to re-learn opening positions, heat up speeds etc...? Or could it be that I should just leave things to settle down for a few days, maybe all my fiddling is causing the HR91 learning to be reset and not adjust?

    Dan
    Glad its not just my system !! I've had mine for over 6 years now and still have this issue in two rooms with two rads. I recently had one rad controller break and replaced it with a new HR92. Previously I had an HR80 and HR92 in the same room. In that set up the rad with the HR80 was on more than the one with the HR92. The HR92 was the temp sender so maybe that was to be expected. However, when I changed the UK8 to the HR92, still as the temp sender, suddenly the other rad was on more !! I tried swapping the second to be the temp sender and it still came on more than the other rad. So I ended up putting the new HR92 in another room that had an HR80 so that I could put the HR80 back as the main rad in the two room set up and all is back as it was I have another room that does the same and I have yet to work out what determines why one rad is on and the other off So yes I do believe there is some deep cunning logic built in to two rad room setups and I wish the developers would reveal what is going on (and yes I did try setting up as multi room set up and the results were even more inconsistent!). In case any one wonders why I should be bothered by this as long as the room is a temp, the whole issue I have with this behaviour is that one of the rads is next to the settee and that is the one I want on most of the time as it just feels cosier

  7. #7
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    My lounge has two HR92s on the radiators. Both function together. When we hear one opening we hear the other and both seem to reach the same temperature although I must check that, I could be wrong. The second radiator is behind a settle and yes, it warms your back nicely!

  8. #8
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    I think in my case yes they were both opening, just one a lot less than the other, which I guess was leading to one of the radiators not getting hot. What seems odd, is this is the same behaviour in the other room, and in both cases it was the rad binded first.

  9. #9
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    Quote Originally Posted by daniel@paynefamily.co.uk View Post
    Hi
    So the question is.... When you add multiple radiators to a zone, does Evohome try and be clever by only using 1 radiator when the heat demand is low, say < 40%? What's odd is in both cases the 1st radiators were in cooler parts of the room (proven by them reporting a lower temp where split into 4 zones), yet it was favouring heating only the second radiators to bring the room up to temp.
    No, it doesn't try to be clever and only operate one radiator for low demands. I have one zone with two radiators - one a long 2m radiator the other about 800mm long. I haven't had any problems with them not "tracking" with each other.

    The small one does tend to heat slightly hotter and quicker than the large one but I think that's largely down to the fact that both are fed with 8mm microbore which is a bit marginal in cross sectional area for the large radiator hence a longer warm up time.

    However the turning on threshold of both radiators is very close, with the reported valve pin position of the two HR92's (menu option 10) always within about +/- 5% of each other and I have never noticed one radiator hot and the other cold in the year that room has had two radiators.

    What you have to keep in mind when trying to analyse what's going on in a single room zone with two HR92's is that both HR92's work in parallel autonomously from each other but with the same input data.

    In each 4 minute comms window they are sent the same set point and same measured temperature data from the controller, and they have the same firmware. (There has only ever been one firmware version released for the HR92)

    So you have two devices running the same firmware using the same deterministic algorithms being presented with the same inputs at the same time - so in theory they should track perfectly giving the same initial starting point.

    While they have learning heuristics (they self-tune their PID controller constants over time, especially the differential constant) that learning process is also deterministic and should track between the two devices.

    However in practice they don't quite track perfectly because it's possible to throw them out of step with each other for example by rebooting one device, or leaving one device out of action for a while (removed from a radiator) while the other one continues to learn.

    So I can certainly see how they might get out of step. Whether it's possible to reset their heuristics back to defaults I'm not sure.

    When you have one radiator hot and the other cold what are the reported valve pin positions of the two HR92's ? If they are within +/- 5 or so I'd say there was nothing wrong with the algorithmic tracking of them and its more likely a problem with the valve body or the calibration of the valve pin position. In the latter case make sure both HR92's are in the same stroke mode and force a recalibration of both.

    Anyway my post is mainly just to confirm that two radiators per zone can and usually does work just fine and that they should track, however I can see possible explanations for why they might get out of sync with each other especially if you are fiddling with them a lot.
    Last edited by DBMandrake; 28th January 2021 at 09:14 AM.

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