Display shows E5 and the refrigerator may not defrost correctly, with ice forming behind the rear panel.

Danger: The defrost heater operates on mains voltage. Unplug the refrigerator before testing or replacing any defrost components.

• Check for heavy ice buildup: Remove drawers and rear panel in the affected compartment. If the evaporator is encased in ice, manually defrost the unit completely.
• Locate defrost heater: The heater is usually a metal or glass-encased element attached to the bottom or around the perimeter of the evaporator coil.
• Inspect wiring and connectors: Look for burned, melted, or loose connectors on the heater and thermal fuse/thermostat.
• Test heater resistance: Disconnect the heater leads and measure resistance with a multimeter. A very high or infinite reading indicates an open heater that must be replaced.
• Check thermal fuse/defrost thermostat: Locate the thermal fuse or thermostat clipped to the evaporator. Test for continuity at freezer temperature. Replace if open when it should be closed.
• Replace faulty parts: Install a Grundig-compatible defrost heater and/or thermal fuse/thermostat as needed. Ensure all connections are tight and insulated.
• Reassemble and test: Refit the rear panel, restore power, and allow several hours of operation. Monitor for normal defrosting and verify that the E5 code clears.

If the heater circuit tests good but E5 persists, the main control board's defrost relay or triac may be defective and should be checked by a technician.