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Thread: Evohome & Opentherm

  1. #11
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    I have not seen these issues. But then again, I have an OT to eBUS converter between the OTB and my Vaillant Boiler. But low modulation of a boiler becomes quite important with OT. You boiler just seems to be causing self harm in doing that.

  2. #12
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    Quote Originally Posted by bruce_miranda View Post
    I have not seen these issues. But then again, I have an OT to eBUS converter between the OTB and my Vaillant Boiler. But low modulation of a boiler becomes quite important with OT. You boiler just seems to be causing self harm in doing that.
    What you using to do that out of interest? a VR33?

  3. #13
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    Yes a VR33

  4. #14
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    Quote Originally Posted by bruce_miranda View Post
    Yes a VR33
    Does it work OK?

    At some point i'll probably be replacing my boiler with a Vaillant and wondered if it's worth the extra hassle.

    Did you manage to get it to differentiate between CH and HW like it would with the Vaillant controls?

  5. #15
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    On the eBUS side there doesn't appear to be any indication of a difference between the two Heat Demands.
    Hence why I was surprised when @kevinsmart reported in another thread that the OT messages did infact differ. So I will check again.
    However I have implemented different temperatures for CH and HW in a roundabout way. I am monitoring the eBUS side and when I detect that Evohome is calling for HW, I vary the max on the Heating dial scale, that in turn raises or lowers the flow as required. It works extremely well. I can have CH flow set to 55C and then when there is HW demand, I set the flow to 70C.
    Vaillant by default only allows dual temperatures if you use their proprietary eBUS controls. But if you add that in, it overrides the VR33 because there is a eBUS hierarchy and the VR33 is lower than Vaillants own thermostat, that you need in order to use their HW kit.

  6. #16
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    Quote Originally Posted by bruce_miranda View Post
    On the eBUS side there doesn't appear to be any indication of a difference between the two Heat Demands.
    Hence why I was surprised when @kevinsmart reported in another thread that the OT messages did infact differ. So I will check again.
    However I have implemented different temperatures for CH and HW in a roundabout way. I am monitoring the eBUS side and when I detect that Evohome is calling for HW, I vary the max on the Heating dial scale, that in turn raises or lowers the flow as required. It works extremely well. I can have CH flow set to 55C and then when there is HW demand, I set the flow to 70C.
    Vaillant by default only allows dual temperatures if you use their proprietary eBUS controls. But if you add that in, it overrides the VR33 because there is a eBUS hierarchy and the VR33 is lower than Vaillants own thermostat, that you need in order to use their HW kit.
    There's apparently a work around on the Plus System boilers - although i've never implemented it myself. How are you changing the set point using eBus? Some external device I assume.

    'Vaillant HW Priority on EcoTec Pluses

    The vaillant ecotec 6xx boiler can be used as a dual stat boiler.
    Use swithched live on terminal 4 for CH demand.
    Use a volt free contact to short the C1C2 plug on the harness (24V side) to take priority HW demand. Fit a Vaillant VR10 sensor to the orange and black wires of boiler harness to sense cylinder temperature.
    On the first gen ecotecs the temps are set with the dials. On the later models with DIA interface then HW temp is set in the diagnostic parameters.
    Never tried this with a VR33'

  7. #17
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    That's the thing. I have an EcoTec Plus 438, it doesn't even have the 24V inputs on the PCB. Even to get OT to work, I had to play with the terminal 7-8-9, contrary to all advice in the manuals saying NOT TO BE USED in the UK!

  8. #18
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    Quote Originally Posted by bruce_miranda View Post
    On the eBUS side there doesn't appear to be any indication of a difference between the two Heat Demands.
    Hence why I was surprised when @kevinsmart reported in another thread that the OT messages did infact differ. So I will check again.
    However I have implemented different temperatures for CH and HW in a roundabout way. I am monitoring the eBUS side and when I detect that Evohome is calling for HW, I vary the max on the Heating dial scale, that in turn raises or lowers the flow as required. It works extremely well. I can have CH flow set to 55C and then when there is HW demand, I set the flow to 70C.
    Vaillant by default only allows dual temperatures if you use their proprietary eBUS controls. But if you add that in, it overrides the VR33 because there is a eBUS hierarchy and the VR33 is lower than Vaillants own thermostat, that you need in order to use their HW kit.
    Iíve got my new system up and running with my Vokera boiler and it looks like I was wrong, there is no distinction between CH and DHW demands coming from Evohome other than DHW is always max set point. Sorry!

    To workaround I am planning to install a relay to short circuit the outside sensor when the DHW BDR91 closes. From the OTGW Iíll then be able to distinguish, set 70C on DHW, and weather compensate on UFH.

  9. #19
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    Using the max setpoint to determine that DHW is being called for won't give the desired outcome because often the CH demand is also set to the same max by the OTB for no good reason and that is when you definitely do not want to set a higher flow temperature.
    Detecting the DHW via the BDR91 is the sure way to do it and that is what I would have done too. But it was such an easy option for me to do this via software especially since I am constantly monitoring eBUS and Evohome.

  10. #20
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    I am assuming this is the right section to ask this! If I install a Worcester Bosch 8000 Life Combi am I right assuming I need an adaptor to use Opentherm?

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