sensor fault AZ1-BT21 or BT21 — Extract air sensor not connected or defective

What does 21 mean?

The BT21 sensor, monitoring extract air, is not connected or defective. For ground source systems, the pump (AZ1-GP2) in FLM is blocked. For exhaust air systems, this alarm resets automatically.

• BT21 sensor is disconnected or has loose wiring.
• The sensor unit is faulty or damaged.
• Communication problems in ground source installations.

Click steps to track your progress.

1. 1

   For exhaust air systems, wait for the system to perform an automatic reset.

2. 2

   For ground source systems, or if the alarm persists, power cycle the Heat Pump.

3. 3

   Inspect the BT21 sensor connections and placement to ensure they are correct.

4. 4

   If the problem continues, a professional service technician should be consulted.