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Thread: R8810a opentherm bridge with ideal logic +

  1. #1
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    Default R8810a opentherm bridge with ideal logic +

    I took delivery of my evohome system yesterday from evohome shop. Overall I am happy, but at the moment I am having to use the relay box instead of the opentherm bridge.

    The bridge doesn't appear to be powering up. Apparently the LED should flash every second once powered but it doesn't. It also continuously calls the boiler to heat.

    I connected the opentherm bridge to the opentherm connections on the boiler (I have made the connection inside too) but the opentherm bridge doesn't seem to power up. Has anybody else used it with a logic plus? Opentherm was my main reason for choosing evohome as I want the modulating control.

  2. #2
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    Please check with Ideal that that model has OpenTherm enabled. You usually need a patch cable to enable.

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    Also check how how the heat demand has been configured in installer mode SYSTEM DEVICES

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    Thanks for the advice.

    The model is an ideal logic+ 35. It has opentherm and comes complete with the cabling. It just has to be connected internally. Lesser models don't come with the loom, but it comes as part of the weather compensation kit, which I also have. (Spare loom).

    I never tried to configure anything as the r8810 doesn't power up. I'll have another go now and see if I can make any further progress. Perhaps the LED doesn't work in the 8810.

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    Please check it is assigned correctly as I suggested
    Quote Originally Posted by Speedychuck View Post
    Thanks for the advice.

    The model is an ideal logic+ 35. It has opentherm and comes complete with the cabling. It just has to be connected internally. Lesser models don't come with the loom, but it comes as part of the weather compensation kit, which I also have. (Spare loom).

    I never tried to configure anything as the r8810 doesn't power up. I'll have another go now and see if I can make any further progress. Perhaps the LED doesn't work in the 8810.
    I work for Resideo, posts are personal and my own views.

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    I've done as you said, problem is, I can't bind the opentherm bridge, without it being powered.

    I've checked and double checked all the connections, but I can't get the bridge to power up. Do you have any experience with connecting the r8810 to an ideal logic +?

  7. #7
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    Please contact Ideal for advice as it sounds like a connectivity issue with the OpenTherm terminals.
    Quote Originally Posted by Speedychuck View Post
    I've done as you said, problem is, I can't bind the opentherm bridge, without it being powered.

    I've checked and double checked all the connections, but I can't get the bridge to power up. Do you have any experience with connecting the r8810 to an ideal logic +?
    I work for Resideo, posts are personal and my own views.

  8. #8
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    What voltage should be on the opentherm terminals? Ie- what is required to power the r8810?

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    Quote Originally Posted by Speedychuck View Post
    What voltage should be on the opentherm terminals? Ie- what is required to power the r8810?
    It's a loop powered low power digital interface
    I work for Resideo, posts are personal and my own views.

  10. #10
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    I've found some of the info I was looking for by trawling the opentherm standard

    3.3.2.1 Room Unit Current
    Guaranteed current available from the line is the minimum allowable idle signalling current (5 mA). This includes the current necessary to operate the regulator which develops the supply voltage in the room unit.
    Room unit current consumption : 5 mA max.
    3.3.2.2 Room Unit Voltage
    The minimum voltage available to supply the room unit circuitry is a function of the implementation of the room unit communications interface. It is directly related to the Idle Line voltage and to the voltage drops associated with the polarity management circuitry and the voltage signalling circuit in idle state.
    As a guide, a nominal voltage of 3.3V is achievable with a low cost implementation of the interface.
    So I'll be checking this later on when I get back. Interestingly, opentherm will call the boiler if there is a dead short on the cables. So that it can operate like a normal boiler using the same control. This appears to be what is happening, so I'm wondering if perhaps I have a fault in the opentherm bridge.

    The boiler unit must support an important installation feature which allows the terminals at the boiler to be short-circuited to simulate a heat demand such as can be done with existing on/off boilers. The boiler unit should interpret the short-circuit as a heat demand within15 secs of the short-circuit being applied. This must be supported by both OT/+ and OT/- boilers.

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