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Thread: OpenTherm VR33 and Vaillant ecoTEC plus 428

  1. #1
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    Default OpenTherm VR33 and Vaillant ecoTEC plus 428

    I have a Vaillant ecoTEC plus 428 boiler and I'd like to use OpenTherm to control the temperature. I have purchased a VR33 module but wanted to check if anyone had successfully used this with my particular model of boiler. Does anyone know if it is compatible?
    I'm aware of the warranty issues but my boiler is out of it's 5 year period now. I also understand there are concerns about self-install and that I'd need to get a qualified person to install or at least test my installation.

  2. #2
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    I have a 438 and have used the VR33 for many years now. The 428 is very similar.
    I might have been the guy that determined how, it could be connected to the 438 because the instructions floating around at the time did not appear to relate to my boiler. It's particularly scary when you are making connections on a terminal block on the boiler PCB, which is clearly marked, DO NOT USE in the UK!

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    That's very helpful - thanks. I was a bit unsure as the VR33 manual shows the cable plugging into a connector marked X32 on the side of the board whereas the board in my boiler has X31 at the end of the board and a different X32 connector near the middle of the board. It also doesn't have any mounting slot to put the VR33 in (although there is plenty of space so less of an issue).boiler-pcb-snip.jpg

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    I used that space on the side, it's got a nice plastic upstand separation from the PCB.

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    If you do not work this out based on the threads I made on this forum, let me know. I can click a photo of my boiler set up. Especially the 230V 3-4 jumper and the jumper that needs to goes in on the 7--8-9 slots.
    When you plug in the module, you can check if the boiler has recognised the module by looking up the eBUS setting. Then you can also work out if the target temperature is being set correctly or not, even without the OTB connected. If you put the jumper on the VR33 the target should be 90C, if you remove it should be 10C

    p.s. I had a picture in my archives.
    Jumper between 3-4, 7-8 and module connected to X31. See location of module housed.
    Attached Images Attached Images
    Last edited by bruce_miranda; 10th March 2021 at 12:59 PM.

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    That's excellent - thanks again. Was there a reason the boiler wiring plug is not in its socket in the photo? I'm guessing that's normally plugged in when in use.

    So I'm assuming the jumpers provide the 'demand' to the boiler on a permanent basis. One thing I wondered about was would this mean the heating pump is running 24/7 with the VR33 just controlling the temperature or does the boiler work out whether it can stop circulating in certain situations?

  7. #7
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    Ignore that. This photo was actually taken as part of a PCB swap, rather than the VR33 install.

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    OT provides a setpoint of 10C, which the boiler considers as OFF and then starts the Pump over run timer from that point on and then the Pump switches off.

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    That's a relief - I had visions of hearing it running all night. Thanks for clarifying.

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    If you have any eBUS Thermostats or the additional boiler controller that is plugged into the boiler faceplate, then those need to come out. The VR33 has quite a low priority in the eBUS hierarchy, so it is rendered useless if you have other competing controllers on the BUS.

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