Display shows E5 and the refrigerator may not defrost; ice accumulates on the evaporator and rear wall.

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

Diagnostic steps:

• 1. Access the evaporator: Remove drawers and the rear panel in the freezer (or refrigerator, depending on model). Defrost any heavy ice buildup first.
• 2. Locate the defrost heater: It is usually a metal or glass-encased element clipped to the bottom or woven through the evaporator coil.
• 3. Test heater continuity: Disconnect the heater leads and measure resistance. Typical values are 50–300 Ω. If the heater is open circuit, it must be replaced.
• 4. Check thermal fuse/defrost thermostat: Many De Dietrich models include a thermal fuse or bimetal thermostat in series with the heater. Test for continuity at room temperature (or when cold, depending on type). Replace if open.
• 5. Inspect wiring and connectors: Look for burnt plugs, melted insulation, or loose spade terminals. Repair or replace damaged sections.
• 6. Verify PCB output: With the unit reassembled and powered (only if you are competent and using proper isolation), a technician can check if the main PCB supplies voltage to the heater during a forced defrost. If not, the PCB or defrost relay may be defective.
• 7. Replace faulty components: Install a new defrost heater and/or thermal fuse/thermostat as required, ensuring correct positioning and secure mounting.