Freezer shows E4 and may not defrost; heavy frost accumulates on the evaporator and air ducts.

Safety first: Unplug the freezer before testing the heater or accessing the main PCB. The defrost heater operates at mains voltage.

• 1. Access the evaporator and heater: Remove drawers and the rear inner panel to expose the evaporator. The defrost heater is typically a metal or glass-encased element at the base or woven through the coil.
• 2. Visual inspection: Look for burn marks, broken heater sections, or melted connectors.
• 3. Test heater resistance: Disconnect the heater leads and measure resistance with a multimeter. Typical values are between 50–300 Ω depending on model. OL (open circuit) indicates a failed heater.
• 4. Check wiring and connectors: Inspect the harness from the heater to the main PCB for heat damage, loose terminals, or corrosion. Repair or replace damaged sections.
• 5. Replace heater if faulty: Install the correct SMEG defrost heater, routing wires as originally and securing them away from sharp edges and moving parts.
• 6. Evaluate control board: If the heater and wiring test good, the defrost relay or triac on the main PCB may be defective. This typically requires board replacement by a qualified technician.
• 7. Manual defrost and test: Fully defrost the evaporator, reassemble, restore power, and monitor for proper automatic defrosting and absence of E4.