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 .