Thermostat displays E12 and may show incorrect date/time or lose schedules

Safety first: No high-voltage work is required for basic troubleshooting, but turn off HVAC power if you remove the thermostat from the wall.

Steps to troubleshoot:

• 1. Verify power stability: Check that the furnace/air handler is not frequently losing power (tripped breakers, loose disconnects). Unstable 24VAC can affect the thermostat clock.
• 2. Re-set date and time: Manually set the correct date and time on the thermostat or via the Emerson app. Monitor to see if it drifts or resets.
• 3. Enable network time sync: If supported, allow the thermostat to sync time from Emerson cloud services by ensuring Wi‑Fi is connected and the app is linked.
• 4. Factory reset: Perform a factory reset to clear any corrupted timekeeping data, then reconfigure.
• 5. Persistent E12: If the thermostat continues to lose time or schedules, the internal clock or backup power circuit is likely failing and the thermostat should be replaced.

When to call a professional: For systems where precise scheduling is critical (e.g., commercial or multi-zone), have a technician verify power quality and replace the thermostat if needed.