Vaillant combi connections

[DIYspanner]

Turbomax Vuw

I was thinking of changing the CH to Open Therm but I looked at the combi board and it doesn't have an OT connection.

Can anyone tell me what the 20v 7, 8 and 9 terminals in the image are used for please. There's no mention in the manual that I can see.

 

[CountryFan]

Vaillant doesn’t support opentherm, only ebus (their own kind of version). 789 are 20v connections and clearly states DO NOT USE THESE.

 

[DIYspanner]

Of what I've read, the Honeywell T3R, which I installed, does have some intelligence built into it which seems to lean towards what OT is designed to do.