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Thread: Viessmann 100W combi (2021 version ) Opentherm

  1. #1
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    Default Viessmann 100W combi (2021 version ) Opentherm

    I just got installed the Viessmann 100-W - 2021 version ( 35 kW Combi B1KF) to go with my Evohome , I selected it because the new (2021) version of the 100-W has turn down capable of reaching 3.2 kW , and it now has the advanced combustion control ( Lambda)from the 200W, and allows some boiler data (flow temperature and burner modulation %) to be read from Vicare app )

    Although it is marked as Opentherm capable, I was aware before buying (and it was confirmed by Viessmann Technical in the UK ) that when in opentherm control, then the max CH flow temperature could not be set and it would default to 82 deg C .

    I connected up the opentherm anyway and indeed the boiler flow temp did go to 82deg C before modulating down the burner .

    I then then entered the boilers service menu and then under b..2 , item 7, "maximum flow temperature limit , heat circuit 1 " , was the value of 82 . Expecting nothing to happen, I changed this to 70 deg C . It worked , with evohome controller demanding 100% (highest CH water flow temperature), the boiler went up to 70 deg C and started to modulate the burner down much to my surprise.


    I had wired up both the a BDR91 bridge and the R88101A Opentherm bridge , in case the opentherm was too wild for my liking as I had expected I would have gone back to the TPI control with the BDR91 . But I am happy to say I will be using opentherm now.

    Only issue observed for me , was cannot engage the "ECO" mode for DHW , boiler seems to keep the DWW at a set point of 50 deg C .

  2. #2
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    Viessmann was one of my options when looking for a new boiler three months ago Viessmann recommended an approved installer who is about 10 minutes away from me and said he could quote but never did and ignored me. I went for Intergas which had been my main choice. I cannot go as low as 3.2kw max for CH, which is what the new Viessmann is noted for, but I can drop to 6.4kW and set it at that some weeks back. No problems at all. Also have dropped the flow temperature to 65C. It works absolutely fine. Out of interest did your installer know about properly setting it, flow and condensing temperatures and power settings? My experience has been that over 95% have little or no knowledge of such (even so called approved installers) and leave boilers installed as they come with default settings. In your case 80C I assume and maximum kW for CH.

    With the Opentherm connection with the Intergas it just happens and works once the bridge is connected. ECO mode I removed. Could not see the need for it and it only burns more gas than is necessary. It might take slightly longer for hot water to reach the tap but the time is marginal and we donít have the boiler firing up every so often just to keep DHW in readiness.

  3. #3
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    That B.2 setting must be new and Viessmann's way of handling the issues that many on this forum have reported.
    Last edited by bruce_miranda; 11th May 2021 at 01:13 PM.

  4. #4
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    3 weeks with the 100-W on evohome opentherm, all working well. I was close to selecting intergas because it has a good opentherm implementation and appears to be an excellent reliable boiler , my only negative was that aluminium is on the acidic condensate which I did not want. The installer did not optimise the boiler for opentherm every thing was left on defaults . After 2 days I reduced the burner output to 45% and set the max CH temperature to 70 deg C (I will soon change this to 65 deg C) .

  5. #5
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    Quote Originally Posted by JCK View Post
    3 weeks with the 100-W on evohome opentherm, all working well. I was close to selecting intergas because it has a good opentherm implementation and appears to be an excellent reliable boiler , my only negative was that aluminium is on the acidic condensate which I did not want. The installer did not optimise the boiler for opentherm every thing was left on defaults . After 2 days I reduced the burner output to 45% and set the max CH temperature to 70 deg C (I will soon change this to 65 deg C) .
    I am sure you will find 65C no different, although with the current weather it wonít be on! My maximum kW for CH remains set at 6.4kW but I canít go lower - you can! During colder months it was never a problem. Aluminium issues I think are more a thing of the past plus there is a requirement to fit a limescale filter with a new boiler and we are fortunate where we are as we have good water, none of the stuff that furs up the kettle!

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