Freezer displays E4 and may not defrost properly; ice builds up on the evaporator and airflow is reduced.

Safety: Unplug the freezer before accessing the evaporator or control board. The defrost heater operates at mains voltage.

• 1. Inspect for heavy frost: Remove freezer drawers and inner rear panel. If the evaporator is encased in solid ice, the defrost system is likely not working.
• 2. Locate defrost heater: The heater is usually a metal or glass-encased element attached to or beneath the evaporator coil. Note its wiring connectors.
• 3. Test heater continuity: Disconnect the heater leads and measure resistance with a multimeter. An open circuit (no continuity) indicates a failed heater that must be replaced.
• 4. Check defrost thermostat / thermal fuse: Look for a small round thermostat or inline thermal fuse clipped to the evaporator tubing. Test for continuity at freezing temperatures; an open device may be faulty (or tripped due to overheating).
• 5. Inspect wiring harness: Follow the heater and thermostat wires back to the control board. Look for burnt connectors, brittle insulation, or broken conductors.
• 6. Replace faulty components: Install Siemens-compatible defrost heater and/or thermostat. Ensure good thermal contact between thermostat and evaporator tube.
• 7. Manual defrost: Before restarting, fully defrost the evaporator with warm air (no sharp tools). Mop up meltwater to prevent refreezing around the fan.
• 8. Reassemble and test: Refit the rear panel and drawers, restore power, and monitor for normal frost pattern and absence of E4.

Note: If heater and thermostat test good, the main control board may not be initiating defrost and should be checked by a professional.