Remedy
Check the HMI for display and remove the HMI and the test voltage to the HMI.
Check the white HMI plug on far right of the control unit (low voltage connection).
If using the Key: Check the Key connections (black, white, red, green) are plugged in to the correct position on the control unit. (Next to orange BUS connection leaving one space.) Check the pins on the plug.
Check that the Key is pushed fully home.
Check the batteries of the room control.
For wired room controls check the EMS BUS Voltage to the remote control is 12 - 15V DC.
Check the bridging links are fitted at LR & 230 V out.
Occasionally the Key connection (green flap) can cause this.
Check the 230 V external wiring does not run alongside the BUS connections, thus causing interference.
Replace the control unit.