⚠
warning Honeywell
Error Code Unknown Time
A medium severity alarm indicating the thermostat's real-time clock is not synchronized or contains invalid time data.
? What Causes This
Power loss exceeding 72-hour battery backup, real-time clock battery failure, or time synchronization error.
✓ How to Fix It
- Reconfigure date and time settings.
- Verify 24VAC power supply continuity.
- If issue persists, contact service for RTC replacement.
Source: page 119 of the official manual
From the manual
