Indoor unit displays E4 and stops heating; often occurs in heat pump mode during cold weather.

Safety first: Turn OFF power at the disconnect before opening the outdoor unit.

• Step 1 – Observe outdoor coil: During heating mode, check if the outdoor coil is covered in frost or ice. Some frost is normal, but heavy ice indicates defrost issues.
• Step 2 – Allow automatic defrost: Many Klimaire heat pumps will enter defrost mode automatically. Let the unit run through a full cycle to see if E4 clears.
• Step 3 – Inspect outdoor sensor: Locate the outdoor coil temperature sensor clipped to the condenser coil. Ensure it is firmly attached and not dangling. Check the sensor wiring for damage.
• Step 4 – Clean coil and surroundings: Remove debris around the outdoor unit and gently clean the coil to improve heat exchange.
• Step 5 – Replace faulty sensor: If E4 persists and the sensor is suspect (cracked, corroded, or reading incorrectly on a meter), replace it with the correct Klimaire outdoor coil sensor.
• Step 6 – Board/valve diagnosis (pro): If the sensor is good but defrost does not initiate properly, a technician should test the outdoor PCB defrost logic and the reversing valve operation.