Thermostat displays E8 and may shut down heating or cooling due to detected high temperature at the thermostat or in the equipment.

Safety first: Turn off power to the furnace/air handler at the breaker. Components may be hot; allow them to cool before inspection.

• Step 1 – Check thermostat location: Ensure the thermostat is not directly above a supply vent, near a lamp, or in direct sunlight. If it is, redirect airflow or consider relocating the thermostat.
• Step 2 – Replace air filter: Remove and inspect the furnace/air handler filter. If dirty, replace with a new filter of the correct size and MERV rating recommended by Carrier.
• Step 3 – Inspect vents and returns: Make sure supply registers and return grilles are not blocked by furniture, rugs, or dust buildup.
• Step 4 – Reset system: After correcting airflow issues, restore power and see if E8 clears. Monitor operation for short cycling or unusual noises.
• Step 5 – Check furnace high-limit (advanced): If the furnace continues to overheat and shut down, the high-limit switch or blower speed settings may be at fault. This requires a technician to test and adjust.
• When to call a pro: Persistent overtemperature faults can damage the heat exchanger; have a Carrier technician inspect the furnace if E8 recurs.