Vaillant 831 Eco Tec Plus combi with open therm

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  • garymtitley
    Automated Home Sr Member
    • Feb 2019
    • 59

    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.
  • dty
    Automated Home Ninja
    • Aug 2016
    • 489

    #2
    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.

    Comment

    • garymtitley
      Automated Home Sr Member
      • Feb 2019
      • 59

      #3
      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.

      Comment

      • dty
        Automated Home Ninja
        • Aug 2016
        • 489

        #4
        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.

        Comment

        • garymtitley
          Automated Home Sr Member
          • Feb 2019
          • 59

          #5
          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.

          Comment

          • garymtitley
            Automated Home Sr Member
            • Feb 2019
            • 59

            #6
            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.

            Comment

            • garymtitley
              Automated Home Sr Member
              • Feb 2019
              • 59

              #7
              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; 9 February 2019, 02:03 PM.

              Comment

              • dty
                Automated Home Ninja
                • Aug 2016
                • 489

                #8
                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.

                Comment

                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #9
                  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.

                  Comment

                  • garymtitley
                    Automated Home Sr Member
                    • Feb 2019
                    • 59

                    #10
                    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.

                    Comment

                    • dty
                      Automated Home Ninja
                      • Aug 2016
                      • 489

                      #11
                      Given a modulating boiler, I'm not sure why one would ever limit the max power unless you found this also affected the bottom end (like Bruce has), or else your pump is set too low and can't move the heat out fast enough, thereby causing your boiler to overheat and cut out.

                      Comment

                      • garymtitley
                        Automated Home Sr Member
                        • Feb 2019
                        • 59

                        #12
                        Yes,your right I will leave it set to max as it is modulating so should sort it's self out.Once the boiler is over 15kw the pump speed is on 2,the fastest speed,below that it on 1,the slower speed.The reason I thought about lowering the output is because I think the boiler goes in to anticycle mode after it's been running for a while.

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #13
                          In my case, my boiler was specced too large. My Alpha2 pump and the 22mm heating loop are not man enough to take the heat away from the boiler fast enough. The boiler was originally meant to do a lot more work but with UFH now installed downstairs, it actually needs to do less. If you look at the manual, you'll see that Vaillant use the same board for many boilers. What I didn't realise was, when set as a 18Kw max, it was actually behaving as a 418 even though it's a 438. So it uses the 418 modulation range, sweet....

                          Comment

                          • garymtitley
                            Automated Home Sr Member
                            • Feb 2019
                            • 59

                            #14
                            Hmm,that's given me an idea.I was told that the 831 was a slightly higher spec boiler than the ecotec pro 24/28,the 24 model modulates down to 6.7 from 19kw so it might be worth me trying that,may work,may not but worth a try as I don't think our house actually needs 24 kw.

                            Comment

                            • garymtitley
                              Automated Home Sr Member
                              • Feb 2019
                              • 59

                              #15
                              Just checked and the 831 does indeed share the same pcb board as the ecotec pro 24 and 28.Set the boiler to 19kw,will monitor what happens,fingers crossed it modulates lower.

                              Comment

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