Heater shows E09 and shuts down; may occur during defrost or cold weather

Safety first: Switch off power before cleaning or accessing internal components.

• Check ambient conditions: Confirm that the outdoor temperature is within the heater’s specified operating range. In very cold weather, E09 may be normal protection.
• Inspect evaporator coil for ice: Look for heavy frost or ice buildup. If present, allow the unit to defrost completely by turning it off for several hours.
• Clean coil and ensure airflow: Remove debris from the coil and ensure nothing blocks the air inlet or outlet. Maintain recommended clearances.
• Verify fan operation: Make sure the fan runs at full speed when the compressor is on. A weak or non-running fan can cause coil temperatures to drop too low.
• Restart and monitor: After defrosting and cleaning, restart the heater and observe operation. If E09 recurs quickly, the evaporator sensor or defrost control may be faulty.

Persistent E09 in normal ambient conditions should be investigated by a technician, who can test the evaporator sensor and defrost logic on the control board.