⚠
warning Honeywell
Error Code AC LED Off, DC LED On
Loss of AC power — the standby battery is supplying power to the system.
? What Causes This
AC power failure or disconnection from the wall transformer.
✓ How to Fix It
- Check the wall transformer connection.
- Verify AC power availability at the outlet.
- If AC fails to restore, the system will continue operating on battery backup until battery is depleted.
Source: page 2 of the official manual
From the manual
This error code appears in:
Honeywell Pro 5000 Thermostat