Activate login mode:
To activate the login mode on the room thermostat, open the menu with the menu button (M) and select with the settings button 
System settings. 
Open the 9-9-1 menu.
The number of registered DuoFern devices is displayed. In our example, one device is logged in.
Switch the respective DuoFern device to the login mode.
Start the login process with the settings button.
On flashes in the display.
After successful registration, the new number of registered devices appears.
Log on the next DuoFern device or return to the menu selection using the menu button (M).
Note! Setting DuoFern mode - DuoFern receiver
If the room thermostat is registered with the HomePilot® , the DuoFern mode should be changed to receiver on the room thermostat. The room thermostat also has a complete time program via which heating phases can be set. By switching to receiver, the room thermostat's own switching time program is deactivated.
Menu item 9-9-2 to 1 (receiver)