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Thread: Converting wired Y plan to Opentherm

  1. #1
    Automated Home Lurker
    Join Date
    Nov 2006

    Default Converting wired Y plan to Opentherm

    I have a fully wired Y plan system, set out exactly as in the Evohome wiring guide:

    Y plan wiring.JPG

    What I am trying to get my head around is what changes need to be made to convert this to O/T boiler control, as opposed to BDR91. At present the CH demand BDR91 is remotely located from the boiler, and has been wired into the previously removed room thermostat. I have two controllers, one bound with the hot water kit setup and the second, just CH, bound to the BDR91 a boiler demand.

    Having upgraded from Hometronic to Evohome, I am much impressed with the advances that Honeywell has made, and the system is operating like a dream.

    Any guidance much appreciated as I am getting set to upgrade to an Intergas OV boiler.

    Many thanks!

  2. #2
    Automated Home Ninja
    Join Date
    Aug 2016


    I *think* that wiring diagram is a bit confused! There's an odd wire coming out of the side of the DHW BDR which goes via connection 7 to the grey on the valve. I *think* this should actually come from connector B on the BDR. Then, connector B should not go to connection 8, instead the orange wire from the valve connections to connection 8 and onward to the boiler and the pump. Having said that, I'm not an expert on Y-plan.

    In a traditional S-plan setup, it's certainly true that the orange wire(s) from the 2-port valve(s) control the boiler (& pump).

    So... you simply need to disconnect the orange wire (and make it safe because it will continue to be live when there valve is open) and then connect the OpenTherm bridge to your boiler. How to do that depends on your boiler! Then you need to figure out how to control your pump. You could control that from the orange wire, or your boiler may have the pump built in, or an output for driving the pump.

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