Perm. com. error HWC — Permanent communication fault with hot water circulation accessory card

What does 91 mean?

There is a permanent communication fault with the accessory card for hot water circulation (HWC). This issue often points to installation problems, communication circuit faults, or incorrect configuration, blocking HWC functions.

• Communication cables to the HWC card are incorrect or incorrectly installed.
• Fault in the communication circuits within the accessory, input, or display card.
• Incorrect address set on the dipswitch of the HWC card.
• The HWC accessory card itself may be faulty.

Click steps to track your progress.

1. 1

   Turn off the Heat Pump at the main power supply.

2. 2

   Carefully inspect all communication cables connected to the HWC accessory card for proper installation and secure connections.

3. 3

   Verify that the address on the HWC card's dipswitch is set correctly according to the system's installation manual.

4. 4

   Restore power to the Heat Pump and check if the alarm clears.

5. 5

   If the problem persists, contact a qualified NIBE service technician for diagnosis.