Com. fault w. in- verter 421 — Compressor is blocked: Communication fault with inverter

What does 421 mean?

A temporary communication alarm with the inverter has occurred 3 times within 2 hours. This requires a manual reset or has been active for 1 hour.

• A temporary communication alarm has occurred 3 times
• Check the heating medium flow
• Lack of refrigerant

Click steps to track your progress.

1. 1

   Perform a manual reset.

2. 2

   Check the heating medium flow rate.

3. 3

   Verify the refrigerant level.

4. 4

   Inspect communication between the unit and inverter.

5. 5

   Contact a technician if the fault reoccurs.