Thermostat displays E1 and system will not run or runs only in emergency mode

Safety: Turn off power to the HVAC system at the breaker before removing the thermostat from the wall.

• Reboot the thermostat: Turn off the HVAC breaker for 2–3 minutes, then restore power. Check if E1 clears.
• Check ambient conditions: Ensure the thermostat is not exposed to direct sunlight, drafts from supply vents, or heat sources (lamps, electronics) that can cause sensor over-range and trigger an error.
• Inspect thermostat location: If the thermostat is mounted on an exterior wall or near a window, temperature swings can cause sensor issues. Consider relocating the thermostat to an interior wall (this is best done by a technician).
• Physical inspection: With power off, remove the thermostat from the sub-base and inspect for signs of condensation, water damage, or corrosion around the sensor area (usually near the bottom or side vents). If moisture is present, allow it to dry completely and reinstall.

Service note: The internal temperature sensor is integrated into the thermostat control board. If E1 persists, the thermostat typically must be replaced.