Freezer shows E4 and may not defrost, leading to ice build-up on the evaporator

Safety warning: Unplug the appliance. The defrost heater operates at mains voltage and is near sharp metal fins.

Diagnostic and repair steps:

• 1. Access evaporator and heater: Remove freezer drawers and the rear internal panel to expose the evaporator. The defrost heater is usually a metal or glass-encased element clipped to the bottom or woven through the coil.
• 2. Visual inspection: Look for burnt spots, broken heater tubes, or melted connectors. Check the wiring for heat damage.
• 3. Test heater resistance: Disconnect heater leads and measure resistance with a multimeter. A typical heater will show tens to a few hundred ohms. If it reads open (OL), the heater is faulty.
• 4. Check thermal fuse/defrost thermostat: Many AEG freezers use a thermal fuse or bimetal thermostat clipped to the evaporator. Test for continuity at room temperature. Replace if open.
• 5. Inspect wiring to PCB: Trace heater wiring back to the control board. Repair any burnt or brittle sections and ensure connectors are tight.
• 6. Replace faulty components: Install a genuine AEG defrost heater and/or thermal fuse/thermostat as required. Clip them in the same positions to ensure correct sensing and heating.
• 7. Reassemble and test: Refit panels, restore power, and allow a full defrost cycle (often 8–24 hours) to confirm that E4 does not return and ice build-up stops.

Note: If the heater circuit tests good but E4 persists, the defrost relay or triac on the main PCB may be defective and should be checked by a professional.