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  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 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

  6. #6
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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.

  7. #7
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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.

  8. #8
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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.

  9. #9
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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.

  10. #10
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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.

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