Thermostat shows E8 and system reports over‑temperature or overheated control

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

• Step 1 – Check environment: Ensure the thermostat is not exposed to direct sunlight, lamps, or other heat sources. Remove any decorative covers that may trap heat.
• Step 2 – Inspect wall cavity: Remove the thermostat and feel inside the wall opening for unusual heat from ducts, flues, or hot water pipes. If present, install insulation behind the thermostat to isolate it from the heat source.
• Step 3 – Clean vents: Use a soft brush or compressed air to clear dust from the thermostat’s side and bottom vents to improve airflow.
• Step 4 – Reinstall and monitor: Reattach the thermostat and restore power. Monitor the temperature reading and see if E8 reappears.
• Step 5 – Relocate thermostat: If the location is inherently hot, consider relocating the thermostat to an interior wall away from heat sources. This requires rerouting low‑voltage wiring.
• Step 6 – Replace thermostat: If E8 persists in a normal environment, the internal over‑temperature sensor or protection circuit is likely defective and the thermostat should be replaced.