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Thread: Evohome Opentherm - tearing my hair out!

  1. #1
    Automated Home Jr Member
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    Unhappy Evohome Opentherm - tearing my hair out!

    Hi all,

    after taking the plunge of first evohome and then deciding to go upgrade it to opentherm I'm having no end of issues.

    I've got a Vallient boiler using a VR33 module and this interfaces fine with the Evohome opentherm interface - pressing the button switches between 90Deg and 10 Deg draw whichi I can monitor on the boiler.

    However, I could hear the boiler firing a lot even though there was 0% requirement from the zones so I put a temp logger on the flow/return on the boiler, and I was right, throughout the night the boiler is pushing out between 40>60 Deg, despite only one zone being set at 17.5D needing a slight amount to keep it's temp, and certainly not all night needing a draw at these temps.

    I tested the theory and have attached a photo of 0% draw, yet the boiler seeing Ebus target value of 56Deg.20180427_215355.jpg20180427_215335.jpg.

    The signal from the controller to the boiler is perfect (5 flashing red dots).

    In addition to this I've also seen another weird bug, where the kitchen being at 21.5Deg, setpoint at 10Deg, yet it saying it needs 10% pull from the boiler, see below:
    20180428_131618.jpg20180428_131603.jpg

    I love the idea of this system, but at the moment it's seriously failing WAF and is buring way too much gas.

    Are there any hidden screens (beyond the hold setting button for 3 seconds) where I can see more details about what is pulling/sending info where?

    HELP!!

    thanks

  2. #2
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    Do you have any other eBUS controls on the boiler itself?

  3. #3
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    Quote Originally Posted by bruce_miranda View Post
    Do you have any other eBUS controls on the boiler itself?
    Nope just the vr33 to the evohome.

  4. #4
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    Had you just rebooted the controller before you took those last two pictures ? Because an hourglass means it hasn't received a temperature measurement from a zone since rebooting, or hasn't received a measurement in over an hour, the latter suggesting a wireless comms problems.

    Also the controller showing a 0% heat demand for opentherm but the boiler showing a requested temperature of 56C indicates a comms problem. What you are showing is not the way the system should be working so you need to start following the procedures to troubleshoot wireless comms issues.

  5. #5
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    I have a 438, which is an extremely old boiler and the VR33 and OT work well. I am not saying the OT implementation is good but it works. Also you said your kitchen had a set point of 10C but the picture shows 20C. Note the controller rounds up the actual temperature so the 21.5 could easily be a rounded figure and close enough to the set point of 20C for a low Heat Demand.

  6. #6
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    What boiler do you have? I have the same issue with my ecotec pro 28.( demand for heat even when everything is showing 0%). I have taken to limiting the boiler to 55 degrees to reduce the impact.

    I did suspect a comms error but I tried moving the controller next to the opentherm receiver and the problem persisted. I also tried moving the receiver and no change. I only have the problem when one of the zones is within a degree of the set point. I put this down to being by design.

    My main issue was that it seems to ask for a higher temperature, sometimes 75 degrees when at 0%. When a small percentage is being asked for this can be as low as 47.

  7. #7
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    Morning

    Looking at the temp reading this morning I've had another night of Opentherm calling for 40>50 degrees all night, despite all zones being off.
    chart.jpg

    @DBMandrake - yes I'd just rebooted (seeing if that'd fix it), however I took the photos to show how it was before and after the reboot.

    @bruce_miranda - Thanks, however I don't see how an actual temp of 21.5 and a setpoint of 20 should cause any form of draw. 1.5D overshoot and then continuing to call for heat is weird.

    @matjholden - Vallient Ecotec pro 630.

    I'm tempted of deleting everything and doing a full reset, can anyone think of any other options?

    thanks

  8. #8
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    I did just try again a signal test and all looks fine, however one thing which it'd be good for other to check.
    When checking DHW both Opentherm module and BDR91 flash 5 times (full signal), and likewise when checking boiler CH call both again flash.

    Is this what you guys see?

    Also, here is a bit more data on last night. At the bottom is the only room in the house calling for heat, so I can see why the boiler comes on, but what the hell is the massive varience in pull temp for a 17.5deg setpoint?! Surely it shoudl be calling for nearer to 30 to keep that one room constant?

    chart (1).jpg
    Last edited by billytkid; 29th April 2018 at 08:37 AM.

  9. #9
    Automated Home Legend paulockenden's Avatar
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    Just trying to think of something different.... could it be an ABV that’s too slack? A zone might be calling for a tiny amount of heat because it’s in the proportional band (plus or minus 1.5 degrees), but if most of the boiler output was going round the bypass loop the zone would keep demanding more heat.

  10. #10
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    What I have noticed is that when changing from a 10 degree demand the opentherm always requests a 90 degree demand next. This isn't an issue when a number of radiators are demanding heat as after a minute or two the demand is updated to something more suitable but when only one radiator is demanding heat or the opentherm is demanding heat with all the radiators at 0% it causes high flow temperatures hence my decision to set the max ch temp to 55.

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