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Thread: OpenTherm VR33 and Vaillant ecoTEC plus 428

  1. #11
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    I have nothing connected to the eBUS. What do you mean by 'additional boiler controller'?
    My existing system (Y-plan) just controls the demand signal into terminal 4 on the boiler board - which I believe you are saying will need to be permanently looped ON.

  2. #12
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    If you look at your boiler, it comes with a blank face plate. Some installations replace that face plate with a controller for things like scheduling etc. Most don't have it.

  3. #13
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    I see. I'm pretty sure there is nothing 'non-standard' there. Here's a picture of the front panel.boiler-frontpanel-snip.jpg

  4. #14
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    You see that plate with Vaillant printed on it, that is removable and it can be replaced with a controller. You don't have it.

  5. #15
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    Excellent - thanks. Sounds like I'm pretty much set.

  6. #16
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    Are you able to clarify which OpenTherm commands are needed to control the Vaillant heating? I can see that message ID 1 i.e. set CH water temperature is the key one I must use. However, I've seen some examples of code where people are also sending message ID 0 i.e. set status with CH enable on. If I'm using terminal 4 to run the demand to the boiler do I need to send the CH enable status command or can I just use the feed temperature control on its own?

  7. #17
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    Why are you using an external heat demand with OT. OT will handle both. In the Vaillant, 10C Heat request is OFF. By bridging the terminals 3-4, you are telling the boiler that the Heat Demand will be performed by the eBUS device. And then by bridge the eBUS terminals you are telling the boiler than the eBUS device is within the boiler itself I.e the VR33 rather than an external device.
    Last edited by bruce_miranda; 8th March 2022 at 12:11 PM.

  8. #18
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    Yes I know. I did have a separate thread on this. My system is connected using Y-plan and the boiler feeds CH and HW based on the valve position. Most of the time it will be constant demand (i.e. voltage into terminal 4) but when I'm heating HW I need to set the feed temperature high and then revert to TPI control for the heating demand. So I was planning to leave the system wiring to the boiler as is but just add the OpenTherm connection to adjust feed temperature.
    So my main question was whether there were any other OpenTherm commands required to the boiler to do this other than setting the CH feed temperature. In particular does the status message (message ID 0) turn things on and off?

  9. #19
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    Until I had worked out that I needed to fiddle with 7-8-9 to allow the OT to fire the boiler, I was basically doing what you want to do. My boiler was still being trigger via Terminal 4. The OT was simply varying the Flow Temperature because it couldn't trigger the boiler. So you should be fine.

  10. #20
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    Thanks that helps. I'd seen examples of code where people were sending 'set status' commands with 'enable CH' flags set etc. I'll assume my signal on terminal 4 will be enough to fire it and then just set the feed temperature. Once I get it all connected up I'll let you know.

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