Thermostat displays E9 and may reboot repeatedly or freeze

Safety: No high-voltage work is required, but do not open HVAC equipment panels.

• Check mounting location: Ensure the thermostat is not mounted above a heat register, on a wall with hot plumbing, or where direct sunlight hits it for extended periods.
• Improve ventilation: Make sure the thermostat is not sealed tightly against heavy wallpaper or foam insulation that blocks airflow through its vents.
• Shade the thermostat: If sunlight is the issue, install a small shade or relocate the thermostat to an interior wall away from windows.
• Power cycle: Turn off the HVAC breaker for a few minutes, then restore power and monitor operation.

Note: If E9 recurs even in a cool, shaded location, the thermostat’s internal components may be failing and replacement is recommended.