Refrigerator displays E5 and may not defrost properly; ice builds up on the evaporator and airflow is reduced.

Safety first: Unplug the refrigerator. The defrost heater operates at mains voltage and can be hazardous if live.

Steps:

• 1. Inspect for heavy frost: Remove freezer drawers and check the rear panel. A solid block of ice behind the panel is a strong indicator of defrost failure.
• 2. Access heater and safety devices: Remove the inner rear panel to expose the evaporator. The defrost heater is usually a metal or glass-encased element at the base or woven through the coil. A thermal fuse or bimetal thermostat is often clipped to the evaporator tubing.
• 3. Test heater continuity: Disconnect heater leads and measure resistance. A typical heater reads between 50–300 Ω depending on design. An open reading (OL) indicates a failed heater.
• 4. Test thermal fuse/bimetal: With the evaporator cold, the bimetal should read closed (near 0 Ω). A blown thermal fuse will read open and must be replaced with the exact Siemens-rated part.
• 5. Inspect connectors: Look for signs of overheating or melting at the heater and thermostat connectors. Replace any damaged connectors and ensure tight fit.
• 6. Evaluate control board: If heater and safety devices test good, the main control board may not be energizing the heater. This requires board testing or replacement by a qualified technician.

Note: Always replace thermal fuses with the correct temperature and current rating specified by Siemens; never bypass safety devices.