The LED on the front of your Extension Kit tells you what state your Extension Kit is in.
Slow pulsing/breathing
The Extension Kit is working as intended.
Off
The Extension Kit is not supplied with power.
This is usually because your Extension Kit is wired incorrectly. Make sure you double-check the wiring instructions in the tado° app.
Rapid blinking
The Extension Kit is pairing.
Double blink
The Extension Kit is wired and powered, but is not paired yet.
You need to pair the Extension Kit with the Internet Bridge.
If the Extension Kit is not running on the latest firmware, you may notice other blinking patterns on the device. Once the firmware has updated (this is an automatic process), the states should match those mentioned above.