De'Longhi dehumidifier shows E4 and will not run the compressor.

Safety first: Unplug the unit. Coils and metal edges can be sharp; wear gloves.

Step-by-step:

• 1. Power reset: Disconnect power for 5–10 minutes and restart. If E4 returns, proceed.
• 2. Access evaporator/defrost area: Remove the front or rear cover to expose the evaporator coil and tubing.
• 3. Identify defrost sensor: The defrost sensor is usually clipped to the evaporator or suction line, separate from the main evaporator temperature sensor. It is another NTC probe or small sensor module.
• 4. Check attachment: Ensure the sensor is firmly clipped or taped to the coil/tube. Reattach if loose so it senses coil temperature correctly.
• 5. Inspect wiring: Follow the sensor wires back to the PCB. Look for breaks, pinched sections, or signs of moisture ingress. Reseat the connector.
• 6. Replace sensor: If wiring is intact but E4 persists, replace the defrost sensor with the correct De'Longhi NTC probe or sensor assembly.
• 7. Control board check: If a new sensor does not clear E4, the defrost control circuit on the PCB may be defective. PCB replacement is a technician-level repair.