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Thread: Viessmann / Honeywell OpenTherm issue

  1. #1
    Automated Home Lurker
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    Default Viessmann / Honeywell OpenTherm issue

    I have had the dreaded Viessmann Vitodens 100 / Honeywell R8810 OT bridge combination. Sometimes the boiler grinds to a halt with the F:A9 error and we have to power the boiler off and wait. It usually works after a couple of resets – sometime for days on end.

    Other times it appears to clear itself. Presumably there are times when we don’t notice this. When there is a problem I get three flashes of the red light on the R8810.

    It would be good to have a reliable system, but at the moment the OT combination is not fit for purpose. In an old thread StephenC suggested “reversing the telemetry configuration on the Evohome controller” – I’m reasonably savvy but have no idea how I would do this. Does anyone have any suggestions as to how I can get these two bits of kit to work.

    Thanks

    PS Not sure if it’s normal but even when the boiler is working it seems to run very hot. I thought the point of OpenTherm was to have the minimum temperature required.

    PPS Happy to switch off the R8810 if it makes it more reliable, but it would be a shame

  2. #2
    Automated Home Legend
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    Viessmann with Honeywell OT will make your boiler reach for the lofty highs of 85+°C. I don't think you want that. Go back to using a BDR91 as your boiler controller.

  3. #3
    Automated Home Ninja
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    Default

    Viessmann + OT =

  4. #4
    Automated Home Jr Member
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    I read somewhere, can't remember where, that the opentherm gateway http://otgw.tclcode.com/ helps with control of the Viessmann.

    Michael

  5. #5
    Automated Home Legend
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    Yes that will work, but that adds another link to the chain. You need to then send the Max Flow temperature OT command to the Viessmann.

  6. #6
    Automated Home Guru
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    Feb 2017
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    Hi planteric,

    The reversing “telemetry configuration” was a firmware change (rollback) on the evotouch controller. That’s not something applicable unless Honeywell tech support have put your controller into special monitoring mode.

    It does sound from your description however very similar to the specific issues I had during that testing/monitoring/troubleshooting timeframe (OT comms error issues A09 fault code), which to be clear for you and anyone else reading this was separate from the excessive temperatures the boiler was reaching due to lack of max CH flow temp being set on the Viessmann via the controls.

    Can you post your firmware versions?

    Long story short however (even if the comms issue gets sorted) Viessmann boilers and Honeywell EvoHome are not compatible (in the real world) when connected via RR8810 OT controller.


    I’d therefore suggest cutting your losses and going back to on/off control via the default BDR91.
    Last edited by StephenC; 12th February 2019 at 06:49 AM.

  7. #7
    Automated Home Lurker
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    Hi all,

    Apologies for the late reply, and many thanks for your advice.

    After a mere 6 weeks my plumber turned up to remove the opentherm and set the boiler control to NONE. Now all is working fine.

    Lesson learned for me is never to trust a builder when they say their plumber understands evohome and opentherm. Even with Honeywell supporting him my one knew as much as I picked up by googling – less in a couple of instances. I wish I’d googled about the type of boiler that works with opentherm as well. It would have saved me being caught up in the Viessmann / Honeywell blamestorming.

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