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Thread: Evohome Hot water problems

  1. #1
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    Default Evohome Hot water problems

    So this is the 2nd evohome system I've had and the first time i've used the hot water kit, Previous house we just had a combi boiler

    First off getting the hot water kit installed was a nightmare as we couldn't find an installer in south wales. Eventually though using the forum and some help from evohome shop I got it up and running which it worked fine for a week or two until...


    I could hear the tundish activating on the cylinder. Looks like the temp wasn't reporting correctly from the sensor back to the boiler and i thought this was solved by moving unit to a better position in the airing cupboard

    Again this morning i could hear the tundish dripping and after i popped the batteries in unit the temp jump straight away so it looks like the temp isn't being reported correctly back to the controller. As i work offshore my wife tells me this is actually a regular occurrence

    I've tried moving the unit, changing the batteries and also playing with the battery tension

    From looking at the past history it seems the hot water kit is very temperamental

    Any thoughts on what to try next?

  2. #2
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    I've had a faulty one before now, swapped out and seemed much better.

    Batteries have to be around 1.6v, soon as they start dropping south to 1.5v unit plays up.

    Make sure battery tensions are tight and repair with Evohome.

    Have you not left the Cylinder Stat/High limit stat wired in so if it fails the system cuts out anyway? It's a requirement of regs.

  3. #3
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    Quote Originally Posted by mtmcgavock View Post
    I've had a faulty one before now, swapped out and seemed much better.

    Batteries have to be around 1.6v, soon as they start dropping south to 1.5v unit plays up.

    Make sure battery tensions are tight and repair with Evohome.

    Have you not left the Cylinder Stat/High limit stat wired in so if it fails the system cuts out anyway? It's a requirement of regs.
    i've tried changing the batteries for some duracells still the same problem thought

    Stat/High limit is still wired in, i left that part all in place

    Maybe the unit is faulty which is annoying as it's not very old

  4. #4
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    Quote Originally Posted by crh View Post
    i've tried changing the batteries for some duracells still the same problem thought

    Stat/High limit is still wired in, i left that part all in place

    Maybe the unit is faulty which is annoying as it's not very old
    Your discharge shouldn't really be dripping then, the Safety Valve will only blow off at 90oc and that's highly unlikely as one, your boiler would struggle to get to this and two, either the existing cylinder stat or high limit will be kicking in. Sounds like it's letting off on pressure, so sounds like your unvented wants a recharge...

    In terms of not receiving updated temps, when it's unresponsive if you press the button on the front of the HW receiver does the panel get an updated temperature?

  5. #5
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    Quote Originally Posted by crh View Post
    So this is the 2nd evohome system I've had and the first time i've used the hot water kit, Previous house we just had a combi boiler

    First off getting the hot water kit installed was a nightmare as we couldn't find an installer in south wales. Eventually though using the forum and some help from evohome shop I got it up and running which it worked fine for a week or two until...


    I could hear the tundish activating on the cylinder. Looks like the temp wasn't reporting correctly from the sensor back to the boiler and i thought this was solved by moving unit to a better position in the airing cupboard

    Again this morning i could hear the tundish dripping and after i popped the batteries in unit the temp jump straight away so it looks like the temp isn't being reported correctly back to the controller. As i work offshore my wife tells me this is actually a regular occurrence

    I've tried moving the unit, changing the batteries and also playing with the battery tension

    From looking at the past history it seems the hot water kit is very temperamental

    Any thoughts on what to try next?
    I have been using Evohome with the hot water sensor and relay for 5 years and not had any problems other than needing to replace the batteries a little more often than with the HR92 head units although that is not so bad since I ensured there was more tension in the battery compartment to hold the batteries. A common issue with both the control panel and HW sensor.

  6. #6
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    Quote Originally Posted by mtmcgavock View Post
    Your discharge shouldn't really be dripping then, the Safety Valve will only blow off at 90oc and that's highly unlikely as one, your boiler would struggle to get to this and two, either the existing cylinder stat or high limit will be kicking in. Sounds like it's letting off on pressure, so sounds like your unvented wants a recharge...

    In terms of not receiving updated temps, when it's unresponsive if you press the button on the front of the HW receiver does the panel get an updated temperature?

    Thanks for the info and that's really good to know,

    do you mean regenerating the bubble?

    If i press the button on the front it flashes green and red and i think the temp is updating

  7. #7
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    Quote Originally Posted by mtmcgavock View Post
    Have you not left the Cylinder Stat/High limit stat wired in so if it fails the system cuts out anyway? It's a requirement of regs.
    Any advise as to how to do this, my mechanical cylinder stat was removed.
    I have an s plan system

    Thanks
    Last edited by edhodges1984; 29th December 2019 at 09:31 PM. Reason: Error in post

  8. #8
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    Quote Originally Posted by edhodges1984 View Post
    Any advise as to how to do this, my mechanical cylinder stat was removed.
    I have an s plan system

    Thanks
    What cylinder do you have?

  9. #9
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    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!
    Last edited by DBMandrake; 10th January 2020 at 02:08 PM.

  10. #10
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    Quote Originally Posted by mtmcgavock View Post
    I've had a faulty one before now, swapped out and seemed much better.
    Me too, better (the first one was totally unusable) but not problem free by any stretch.
    Batteries have to be around 1.6v, soon as they start dropping south to 1.5v unit plays up.
    My experience as well. Brand new batteries at 1.6v each seem to work OK (at least for a month or two) but as soon as the voltage drops a bit even to 1.5v a cell - which is completely normal with alkaline, which are designed to be used down to about 1.2 volts, it starts playing up and gets progressively more unreliable over time.

    Will Honeywell ever acknowledge or fix this design flaw that the CS92A doesn't work reliably at <1.6 volts per cell ? Probably not.

    In my long thread from a couple of years ago where I tried to dig into this problem deeply I concluded that part of the issue was related to the power saving mechanism in the device acting inappropriately.

    It has a fairly complex power saving algorithm which takes a number of factors into account when deciding how often to send temperature updates. One is the temperature range - the CS92A apparently knows what the hot water set point and differential is configured to, and will send "frequent" updates when the temperature changes within this range, but very infrequent updates when the temperature is outside that range.

    In my case with a set point of 54 and 5 degree differential I get frequent updates between 49 and 54 degrees. Below 49 degrees they are very infrequent, and this is plainly evident looking at my graphs. One issue is that sometimes the set point and differential between the controller and CS92A can get out of step if you ever change the settings in the controller, this can cause part of this differential temperature range to now land outside the "frequent" update range.

    In particular if you increase the set point slightly and that doesn't get communicated to the CS92A properly it can cause massive overshoots as there can be a delay of 20 minutes or more before the final temperature increase is communicated, by which time an overshoot has occurred.

    It's not clear to me exactly what you can do to get them back into sync again in this situation, (as it doesn't fix itself) whether it's to reboot the controller, the CS92A, or just re-configure the set point a couple of times. In my testing I wasn't able to determine the best course of action when the situation arises, and it took lots of "fiddling around" with all of the above to fix the problem without ever really being sure which action fixed it.

    Outside of the "frequent updates" temperature range it seems to vary the frequency of updates based on battery voltage. A high battery voltage allows "moderately frequent" updates even outside that differential range but as the battery voltage gets lower they become less frequent until the point where problems start to occur.

    If the temperature is near constant outside the frequent update range (normally when the hot water is off and has fallen well below the differential band and reached a semi-equilibrium) then it seems to be normal for the sensor to send an update as infrequently as hourly. However to cause the hourglass to appear on the controller and an error to be logged requires no temperature updates to be received for three hours, and I can't see any good reason why the sensor wouldn't send anything for over three hours even if it thinks the battery is a bit low.

    Most reports of lost comms with the sensor reported here not surprisingly occur when the hot water is scheduled off and the temperature has fallen well below the differential band, for example overnight.

    All these problems could easily be addressed by a revision to the CS92A - fix the voltage sensitivity issue, fix the differential band overshoot issue (by giving a bit more margin at the high and low limits) and make sure that an update is sent at least hourly even if there are no temperature changes. (I suspect that's already meant to be the case but a bug may be preventing it)

    When so many people report the exact same problems there's clearly a problem here.
    Last edited by DBMandrake; 10th January 2020 at 02:33 PM.

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