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Thread: New home, mammoth Evohome install

  1. #41
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    I learned that my boiler’s floor heating jumper tag setting is actually dynamically read.

    If the jumper is inserted, OpenTherm will switch from a 40-80C range to 20-45C.

    So, I’m going to connect an Arduino relay to the OTGW GPIO. When there is a demand for less than 40C, I’ll program the OTGW to close the relay.

    Will be interesting to see if this reduces some cycling when zones are near their set points.
    Last edited by kevinsmart; 6th February 2021 at 03:37 PM.

  2. #42
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    What boiler are you running Kevin?

  3. #43
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    Quote Originally Posted by bruce_miranda View Post
    What boiler are you running Kevin?
    Vokera Unica, and LPG, unfortunately Bruce. Will probably make do with it until the time is right to fit a GSHP.

  4. #44
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    I’ve added my OTGW controlled Arduino relay to switch my boiler between standard heating (40-60C) and floor heating (20-39C) modes. Appears to work well.

    Conveniently the OTGW has 4 pins above the PIC: GND, GPIO2, GPIO1, 5V perfect for this application. I added a 4-pin header cable to control the relay and a 2 pin male from the relay to bridge the boiler’s jumper.

    So, I think that’s the install all done now, will monitor how it runs.

  5. #45
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    So it turns out, after all that, that floor heating mode doesn’t work very well for my setup.

    In this mode the boiler appears to reduce its hysteresis from +5/-5 to +2/-2C.

    What this means, with low temperature requests, is that the boiler ignites and immediately exceeds its upper temperature limit, shutting down, anti-cycling for 3 minutes, and repeating.

    So, I gave up on that idea.

    Now I’m taking advantage of my Vokera boiler supporting reading of its return water temperature, unlike Intergas.

    If the return water temperature exceeds the control setpoint I set CH mode off until it reduces.

    So now rather than my boiler running for hours at 40C with OpenTherm requests < 30C, it will periodically heat and then turn off earlier.

  6. #46
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    Hi Kevin

    What exactly did you do to make a 10c request actually switch-off the boiler? I've got some pretty good OpenTherm optimisations working via Home Assistant but I'm having trouble making the 10c take effect as it just appears to be ignored by the boiler whilst the controller still has heating mode active. I can see the request being acknowledged within the OTG messages log.

    Also have you had any issues with max modulation being ignored. Again I can see my request has been acknowledged and is showing up in the OTG but appears to have no effect.

    Thanks!

  7. #47
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    10C in OT generally means OFF. So I didn't think you have to do anything specific to make the boiler go off with a 10C target temperature. Unless you are saying that your 10C target is not sticking and so the boiler stays on.

  8. #48
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    Yes, this initially confused me as well. A 10C request is used by Evohome to signify off, but by default, if CH Enable is on, it will be interpreted by my boiler just like any other request below 40C. The boiler will heat to its minimum control set point of 40C.

    So, you have to set CH Enable to disabled, that turns the burner off, and in this case it doesn’t really matter what the control set point is, so no need to set 10C.

    But the other important aspect is still to report to Evohome that CH Mode is on. If you don’t, Evohome gets confused and appears to try increasingly higher set points, probably until it sees the burner ignite.

    I can advise you of some code if you are doing this in OGTW.

    Regarding maximum relative modulation my boiler ignores any setting.

  9. #49
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    Quote Originally Posted by kevinsmart View Post
    Yes, this initially confused me as well. A 10C request is used by Evohome to signify off, but by default, if CH Enable is on, it will be interpreted by my boiler just like any other request below 40C. The boiler will heat to its minimum control set point of 40C.

    So, you have to set CH Enable to disabled, that turns the burner off, and in this case it doesn’t really matter what the control set point is, so no need to set 10C.

    But the other important aspect is still to report to Evohome that CH Mode is on. If you don’t, Evohome gets confused and appears to try increasingly higher set points, probably until it sees the burner ignite.

    I can advise you of some code if you are doing this in OGTW.

    Regarding maximum relative modulation my boiler ignores any setting.
    This appears to be exactly what's happening, only difference is my boilers min temp is 33c. I'll email you separately about the firmware. Thanks.

  10. #50
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    Quote Originally Posted by bruce_miranda View Post
    10C in OT generally means OFF. So I didn't think you have to do anything specific to make the boiler go off with a 10C target temperature. Unless you are saying that your 10C target is not sticking and so the boiler stays on.
    Sticking, just appears to be being ignored.

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