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Thread: Vaillant 831 Eco Tec Plus combi with open therm

  1. #1
    Automated Home Jr Member
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    Default Vaillant 831 Eco Tec Plus combi with open therm

    Hi,wanting to know if it's worth having open therm on the Vaillant 831 Eco Tec plus combi,I know the vr33 will fit and work with my boiler.This being run by a Honeywell evohome and zoned using the hr92 trv's on all rads bar a towel rad in the bathroom.System seems to run well as is,but would like to be able to try and keep the boiler condensing all the time if possible but before I start spending more money,just wanted people's thoughts on this,those who have done the same.Hope this all makes sense.

  2. #2
    Automated Home Ninja
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    I have a Vaillant EcoFit Pure 625. It modulates down to 6kW. It would be interesting to see what you 831 will modulate down to. This is by far the most important number for efficiency. The longer and slower you can keep the boiler going, the better. Mine obviously still cycles if it requires less than 6kW to maintain the required temperature.

    Having said all that, it works well on OpenTherm and I often see requested flow temperatures in the 40's during spring and autumn and mid-high 50s right now.

  3. #3
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    Hi,the figures are 8.7-24 kW.Do you have yours set on max,mine is set to 20 KW at the moment,1926 house,cavity wall
    downstairs with solid brick upstairs.The cavity wall has insulation and 300mm of insulation in the loft.

  4. #4
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    I think it's set on Auto. I'm not sure what this even means, to be honest! I experimented with it and it didn't seem to change anything obvious.

    Right now, mine is running at 61C and it's nearly 7C outside. It spend most of the time from lunch time until about 3pm running at 51C. The sun has vanished now, so we're losing the benefit of solar warming. Overnight, when it got down to -4C, it was running at 55C to keep the house at 18C.

    Our house is large - about 4000sqft - with a mix of reasonable insulation and poor insulation, but I believe it has cavity wall insulation all round now.

  5. #5
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    Think auto is max then it modulates down to what's needed,mines an older boiler and you have to manually set the output then it modulates down from there.You get a good flow temp from your system and it goes lower than mine but I think it going to be worth doing,open therm that is,because mine doesn't seem to be condensing as much as I'd like.

  6. #6
    Automated Home Jr Member
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    Ordered a Vr33 open therm bridge today from Holland,just need the Honeywell open therm bridge and then I can get this installed,will post updates once done.

  7. #7
    Automated Home Jr Member
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    Installed the vr33 and the open therm bridge,set boiler to max kw and flow temp,not sure that's correct but the boiler seems to be doing what it should.Not sure if I should turn the boiler stat down.Will keep a eye on things and see how it goes.The job was very straight forward to do,checked the boiler to make sure it had detected the vr33,it had,bound the open therm bridge,very easy.Took less than an hour to complete.
    Last edited by garymtitley; 9th February 2019 at 01:03 PM.

  8. #8
    Automated Home Ninja
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    Mine is set to auto, but I don't have the flow temp set to max - I have it at 75C. Bear in mind that Evohome will just call for 90C whenever any zone is more than 1.5C below temperature and you'll realise that you can end up with VERY hot radiators if you're not careful! Fortunately, unlike some boilers, the Vaillant will respect the configured max flow even when being controlled by OpenTherm.

  9. #9
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    I have a 438 which doesn't have the Auto KW setting. I have the boiler set to 18KW max. And most of the time it never uses that. To my pleasant surprise, the boiler appears to modulate to a lower bottom end, when I limited the upper end to 18KW. It's goes down lower than when it was set to 28KW.
    Because I am able to sense when the HW is calling, I vary the flow temperature max on the boiler between 60C and 75C. Because I am on an S Plan, I am sure this probably creates havoc with the learning. But my HW rarely kicks because it's topped up by Solar.

  10. #10
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    Yes,I quickly found that out and set the max in the boiler to 65 degrees as when set at 75 degrees which is my boilers default max,the radiators got far too hot and I have two children,could be very dangerous.Seems to be working fine,will give it chance to settle in and make any adjustments later on.My boiler doesn't have auto setting for the output,so set it to its max at 24kw,as the range rating is 8.7-24 and thought that if I lower the max down it might not work so well,don't know if my logic is correct though.

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