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Thread: Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

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  1. #10
    Automated Home Legend
    Join Date
    Jul 2014


    Quote Originally Posted by StuartG View Post
    I have a Vaillant 637 system boiler running with the VR33 and OpenTherm bridge.

    In my case I removed the existing 230V connection that was wired to the BDR91. I connected the VR33 to the expansion board on the side (for me, X31). I also had to reinstate a jumper on the 24V RT connection (for me this was X100, coloured white, and labelled RT24). The boiler installation instructions explicitly say to REMOVE that jumper when using 230V controls. There was a handy little piece of wire in the VR33 box that did just the job. The VR33 instruction (assuming I read the Dutch properly!) don't seem to specifically point this out, presumably because the module could go in various boilers. The installation manual my boiler does say that RT24 might also be labelled X106.

    I too get a confirmation on diagnostic code 90, so it sounds like the module has been recognised.

    I don't know the specifics of how the wiring works inside the boiler, but I am guessing that in the absence of the RT24 jumper then the circuit is broken and hence the boiler never fires up? My understanding is that shorting the OpenTherm connection itself should cause the boiler to fire.

    Hope this helps!
    I too think it's something to do with the 24V connection, but on my boiler it's not marked as such. There are 24V connections called 7 8 9 but the UK never had any controls that used those. There are some boilers that had to switch a diagnostic code (d.20) to switch the boiler from On/Off to Opentherm. But again nothing on that for me.
    My entire installation and all the signs seem to suggest that my OpenTherm module VR33 is installed correctly and is talking nicely to the boiler. No error codes and all the lights are flashing as they should.

    I feel I am close, but yet very far!
    Last edited by bruce_miranda; 10th April 2016 at 10:16 PM.

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