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Thread: Vaillant 831 Eco Tec Plus combi with open therm

  1. #11
    Automated Home Ninja
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    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.

  2. #12
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    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.

  3. #13
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    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....

  4. #14
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    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.

  5. #15
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    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.

  6. #16
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    Do you have an indication to know what the current heat output is? I was only able to derive this once I was monitoring the eBUS.

  7. #17
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    Hi,I don't unfortunately and my knowledge is quite limited as far as that goes.What would I need to do in order to see the required information from the ebus.

  8. #18
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    It's a bit crap of Vaillant to do that, isn't it? Your 438 is clearly capable of a lower bottom end than it would normally use. Why not allow it to use all the range it's capable of? Marketing BS, if you ask me.

    Of course, with eBus monitoring and other factors in play, you *could* dynamically change the max power setting as well to take advantage of this fact in the same way that you change the max flow temperature.

  9. #19
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    Bit of an update,boiler set to 19kw,flow 60 degrees on the boiler.Seems to be working well,getting longish burn times with return temps at the moment in the low 50s,the most important thing is everything is getting up to the set temps and it was near on 0 degrees last night and reaching them as normal.Im hoping that once it's settled in the return temps might drop a bit lower,but for now I'm more than happy.

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