Nuki Opener with Siedle HTA 711 0

Hi all,

i failed to install my Nuki Opener with a Siedle HTA-711-0.

Current state: Door-Buzzer is functional, Doorbell is not detected

Please find attached my current installation.

According to Nuki instructions the doorbell signal is on “7” (two red cables in my case), but my doorbell is still functional when 7 is unplugged. In contrast if I unplug the two grey cables from “c”, the doorbell goes silent. I suspect my 40 year old installation is a bit off from how it should be?!?!

Anyway, I tried those two scenarios:

  1. As stated in Nuki instructions.
    Remove red cables from “7”, connect them with Nuki-Yellow, attach Nuki-Green with “7” instead.
    -> DoorBell not detected by Nuki. DoorBell is functional all the time (even in intermediate installation steps)

  2. Remove grey cables from “c” (-> door bell silent), connect grey-cables with Nuki-Yellow, attach Nuki-Green with “c” (-> door bell functional again!).

In both scenarios the doorBell is not detected by Nuki. What am I doing wrong?