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Thread: Observations with using the Opentherm Gateway as a monitor and Boiler max

  1. #1
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    Default Observations with using the Opentherm Gateway as a monitor and Boiler max

    I finally plugged in my OTGW device that has been sitting in the box for over a year. My set up is the Evohome OTB is plugged into the VR33 (OT <-> eBUS) on a Vaillant 438 boiler. For the last couple of days, I have the OTB passing through the OTGW before going to the VR33.

    I have the OTGW set up as a Monitor only, which in theory is supposed to pass messages unchanged. However what I have noticed is the simple presence of the OTGW in the chain sets the max boiler flow requested temperature to whatever is set as a default on the OTGW. So I am no longer seeing the 90C heat requests on the boiler.

    I have been lucky that the Vaillant has always allowed me to clip the max temperature based on the knob in the front. But I just thought that might be a solution for anyone wanting to use the Evohome OT Bridge but where the boilers are expecting the "Optional" Max temperature to be set, but the OTB doesn't set it. This causes those boilers to just ramp up as far as near 90C as physically possible.

  2. #2
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    This function should always have been available with an Evohome/OpenTherm setup.

  3. #3
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    It's not a mandatory function according to the OT specs.

  4. #4
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    Quote Originally Posted by bruce_miranda View Post
    It's not a mandatory function according to the OT specs.

    That's true, but I think real life use has shown they made a mistake in their specs.

    As a flagship product there should be enough OpenTherm options available to provide a thorough rather than basic degree of functionality, in my opinion.

  5. #5
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    There is a definite change of behaviour that I have noticed by introducing the OTGW into the chain, EVEN when the OTGW is definitely in Monitor mode. There is one radio message that I have seen simply stop between the Controller and the OT Bridge when the OTGW is added.

  6. #6
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    Which message stops with the OTGW connected?

  7. #7
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    The controller queries the OTBridge ever minute and the OTBridge responds with the Boilers Relative Modulation Percentage and the FlameOn Status. As soon as you put the OTGW onto the OT Bus, even in Monitor mode, the Controller just stops querying the OTBridge for this information. The controller won't start querying it again, until the OTGW is removed and the Controller is rebooted. It caused me a lot of head scratching while I was trying to decode all the OT messages between Controller and the OTBridge.

  8. #8
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    Do you still see the OTBridge requesting that information from the boiler? I canít monitor the Controller messages but do see these requests from the bridge with the OTGW connected.

  9. #9
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    Good question. Which is the message that goes between the OTB and the Boiler that shows the FlameOn Status? Relative Modulation comes back to the evohome controller via two messages, once every 5 minutes via MsgID 17. But then it also gets back to the controller every minute in combination with the FlameOn status. It is this every minute comms that seems to stop between the Evohome controller and the OTB, as soon as the OTGW is connected.

  10. #10
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    I see MsgID 17 Relative modulation level every minute.
    MsgID 0 containing Flame status almost every second.

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