Error Code No Ac

AC power has been cut off and the system is operating on backup battery power.

? What Causes This

Loss of AC power to the system.

✓ How to Fix It

Check that the system power cord is securely connected to a working outlet. If AC power does not return, contact your service provider. The system will continue to operate on backup battery until AC power is restored.

Source: page 10 of the official manual

From the manual

This error code appears in:

Honeywell Vista-20P Security System