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Thread: Evohome Hot water problems

  1. #11
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    I have regularly said my system works fine but in fairness I should say I do, sometimes see messages in the Control Panel log that hot water sensor contact has been lost. On reflection yes, they happen when the hot water is not meant to be on. I just ignore them taking the view that sometimes signals do not always get through. It does not cause any problems. I had no hot water a couple of days ago but that was down the valve (a Honeywell one!) not operating properly. Flicking the control lever back and forward a few times freed it up. Certainly not an Evohome issue.

  2. #12
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    Quote Originally Posted by G4RHL View Post
    I have regularly said my system works fine but in fairness I should say I do, sometimes see messages in the Control Panel log that hot water sensor contact has been lost. On reflection yes, they happen when the hot water is not meant to be on. I just ignore them taking the view that sometimes signals do not always get through. It does not cause any problems. I had no hot water a couple of days ago but that was down the valve (a Honeywell one!) not operating properly. Flicking the control lever back and forward a few times freed it up. Certainly not an Evohome issue.
    Depending on when it happens, a loss of comms causes me one of two problems.

    1) If it happens while hot water is off, the system will refuse to heat the hot water -> cold water
    2) If it happens after hot water has started heating it will not shut off -> scalding hot water.

    Apparently scenario 2 played out today as I just got a text from my other half to say that the hot water was reporting 61 degrees.... (my set point is 54) Here is my graph for the period of time:



    The first oval from about 7:30 to 9:00 am is suspicious - no temperature drop reported despite hot water being off and being within the differential band. Normally I would see a gradual reduction over this time not a flat line then a sudden drop. (Nobody was at home during this time to use hot water) This looks like a comms outage of approximately 90 minutes - not long enough to log a fault.

    Around 10am it flat-lines again for a full 3 hours meaning no comms for 3 hours. The controller would have logged the NaN and a fault at around 1pm, as the disappearance of the green line is a result of an invalid (Not a Number) temperature being reported to my script.

    Unfortunately at 12pm I had turned the heating and hot water on remotely and the last known temperature was <49C so from 12pm onwards the hot water would have been heating with a loss of comms from the CS92A. At around 2:40pm it has finally checked in and reported 61 degrees - after heating for a full 2 1/2 hours and finally at this point it would have closed the hot water zone valve... Fortunately the flow temperature is only set to 70 so it can't get much hotter than this, (and it's an open vented cylinder) but 61 is still near scalding temperature.

    Total contiguous comms outage time about 5 1/2 hours from 10am to 2:30pm. No problems with any other zones or BDR91's.

    I'll check the battery voltage when I get home but I bet its still around 1.4-1.5 volts per cell which is perfectly normal for Alkaline and satisfactory for every other piece of AA operated equipment in the world....
    Last edited by DBMandrake; 10th January 2020 at 03:35 PM.

  3. #13
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    Checked the signal - 4 flashes out of 5.

    Checked the battery voltage - both cells are 1.496 volts. Perfectly normal for an Alkaline battery (still about 80% life left) but down into the range where we know the CS92A starts to misbehave. Sigh.

  4. #14
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    Quote Originally Posted by DBMandrake View Post
    Once again I have a problem with the hot water sensor on my system. The CS92A is definitely the most unreliable part of an Evohome system.

    Not sure what the cause is yet as I'm at work but I switched the heating on remotely for my other half who is going home early (another story - the total connect app frequently signs us out on our phones and she doesn't know the password to re-enter so it was easier for me to just do it) and not long after that the hot water temperature is "NaN", and my graphs show no updates from the sensor for over 3 hours. The rest of the system is working fine but I know the hot water will be luke warm when she gets home as the system will refuse to heat it when when the temperature reading goes to "NaN".

    I can predict what the situation will probably be though from the past 10 or so times it has happened in the last year or two alone. There will be no reports of low battery on the controller, just the report of no communication from the sensor and an hourglass for the temperature. If I press the signal test button on the sensor it will give me a 4/5 or 5/5 result. If I remove the batteries and refit them it will miraculously start working again, and if I measure the voltage of the batteries they will be fine and well within spec for Alkaline batteries.

    I've already replaced the CS92A once under warranty (the first one was much worse) and relocated it twice. I've tightened the battery terminals behind the PCB. I always keep fresh batteries in it and don't let them get too low as I know it's unusually sensitive to low voltage. I think next time I change the batteries I'll fit Lithium to pander to its unusual sensitivity to anything other than brand new 1.6v battery voltage.

    I think most of us can agree it's fundamentally broken in design and has systemic problems as all the hot water sensor problem threads here attest, including a thread of my own where I analysed the problems in great detail a couple of years ago around the time I got a warranty replacement. Please Honeywell, if you do nothing else, fix the design of the CS92A. It really is unreliable!
    My own system I never have any issues with, other than once when the batteries were low - as to be expected. Again others I have had no issues at all with.

    I have one customers who used to intermittently drop out, however his might drop out for 20 minutes or so and then reconnect without any input from the user (Just flash a Comms error on the screen). This was the one that I had replaced under warranty too, the new one whilst not as bad wasn't perfect.

    Perhaps we're looking at this the wrong way, have we ever considered it might be the controller at fault rather than the CS92A - would seem to make sense seeming a replacement CS92A doesn't solve anything.

    The other thing I suppose is interference, however the system I have the issues with the CS92A is in the room directly above the controller...

  5. #15
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    Thankfully I don’t get the problems dpmandrake reports. I get the occasional loss of signal message from the hot water sensor but it never fails to operate when it should nor to switch off when it should and the loss of signal message is always when the system is meant to be off anyway. Which is why it has never caused me concern over the last 5 years.

  6. #16
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    The controller is fine - no issues with any other devices. The CS92A is just poorly implemented IMO.

    My original one was far worse, the replacement one has been a lot better, (but not problem free) this might suggest a quality control issue (particularly with the battery contacts, same with all other Evohome devices) but I've also identified some basic design flaws with the way the device decides to send updates that can lead to overshoots in certain circumstances. Well documented in another thread so I won't repeat all the details here.

    If it works for some or even most people then great, however that doesn't mean it doesn't have design flaws that affect some people.

    There's only so many times "interference" etc can be blaimed for comms issues before we just accept that the wireless comms protocol used by Evohome has shortcomings, and that the CS92A in particular takes battery saving to the extreme at the expense of causing comms failures. (By not sending updates when it really ought to - over 3 hours without the controller receiving any updates from the CS92A while the rest of the system works perfectly is not "interference")

    Overall I like Evohome but I couldn't recommend the hot water control side of it as the entire control loop from sensor to controller back to BDR91 relay is just too "fragile". I really don't like that control loop having two wireless communication links involved.

    A better way to do it would have been to combine the temperature sensor with the relay so that the Evohome tells the combined device what the hot water set point and differential are, and the temperature sensor directly controls the relay without any wireless comms, then sends the temperature reading back to Evohome for it to control the boiler relay and for informational purposes. In such a design overshoot due to comms issues would not be possible. The boiler might run on a bit longer but the hot water relay would always close at the correct time even if wireless comms were lost avoiding scalding hot water.
    Last edited by DBMandrake; 12th January 2020 at 05:30 PM.

  7. #17
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    Quote Originally Posted by DBMandrake View Post
    The controller is fine - no issues with any other devices. The CS92A is just poorly implemented IMO.

    My original one was far worse, the replacement one has been a lot better, (but not problem free) this might suggest a quality control issue (particularly with the battery contacts, same with all other Evohome devices) but I've also identified some basic design flaws with the way the device decides to send updates that can lead to overshoots in certain circumstances. Well documented in another thread so I won't repeat all the details here.

    If it works for some or even most people then great, however that doesn't mean it doesn't have design flaws that affect some people.

    There's only so many times "interference" etc can be blaimed for comms issues before we just accept that the wireless comms protocol used by Evohome has shortcomings, and that the CS92A in particular takes battery saving to the extreme at the expense of causing comms failures. (By not sending updates when it really ought to - over 3 hours without the controller receiving any updates from the CS92A while the rest of the system works perfectly is not "interference")

    Overall I like Evohome but I couldn't recommend the hot water control side of it as the entire control loop from sensor to controller back to BDR91 relay is just too "fragile". I really don't like that control loop having two wireless communication links involved.

    A better way to do it would have been to combine the temperature sensor with the relay so that the Evohome tells the combined device what the hot water set point and differential are, and the temperature sensor directly controls the relay without any wireless comms, then sends the temperature reading back to Evohome for it to control the boiler relay and for informational purposes. In such a design overshoot due to comms issues would not be possible. The boiler might run on a bit longer but the hot water relay would always close at the correct time even if wireless comms were lost avoiding scalding hot water.
    The solution to your overshooting would be to wire your Cylinder Stat back in series with the BDR91 and set it at 60oc.

    Has replacing the batteries resolved your issue? As you've said the battery voltages attribute to most of the issues with the CS92A.

    I disagree about combining the devices, it's not always possible to have your motorised valve next to the cylinder so that would cause an issue in that situation. However making the CS92A or at least an option to mains power as well as batteries would be a better solution.

    Mine at home as i've said works flawlessly, however I do notice a a lag in temperature updates past my setpoint of 55. If you start drawing off the next point seems to be 35oc, then 25oc, down to 15oc then settles at 11 (If it's set not to reheat). However I've always just put that down the to rate it's loosing heat.

    Again on a reheat, it'll jump up in 10oc then update more regularly near the set point. As i've said in the past on another thread I think 62oc seems to be a fail safe where it does actually knock off finally if no updates get through.

  8. #18
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    I've also had exactly the same problems as DBMandrake. I've gone through all the suggestions (retensioning battery connectors, repositioning etc etc) but nothing worked. After a lot of backwards and forwards, Honeywell replaced the unit as faulty. Replacement unit worked better, but still not ideal IMOH. Temperature updates are too infrequent, often settling down to about once per hour - a couple of showers can easily use up most of the hotwater in this time.

    In the end I ended up wiring in an ESP32 connected to an additional temperature sensor next to the evohome one, and now get minute by minute updates, which are then used by my home automation system to trigger reheat etc.

  9. #19
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    Quote Originally Posted by smar View Post
    I've also had exactly the same problems as DBMandrake. I've gone through all the suggestions (retensioning battery connectors, repositioning etc etc) but nothing worked. After a lot of backwards and forwards, Honeywell replaced the unit as faulty. Replacement unit worked better, but still not ideal IMOH. Temperature updates are too infrequent, often settling down to about once per hour - a couple of showers can easily use up most of the hotwater in this time.

    In the end I ended up wiring in an ESP32 connected to an additional temperature sensor next to the evohome one, and now get minute by minute updates, which are then used by my home automation system to trigger reheat etc.
    Out of interest, what's you differential setting on?

  10. #20
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    Quote Originally Posted by mtmcgavock View Post
    Out of interest, what's you differential setting on?
    Currently at 10 degrees but I did try various values when I was going through the process of trying to find a workable solution.

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