Wine cooler displays E4 and may not defrost properly, leading to ice buildup on the back wall.

Safety warning: Unplug the appliance before accessing the evaporator or any electrical components. Surfaces may be sharp and may contain ice.

Steps to address E4:

• Manual defrost: Unplug the unit and leave the door open for 12–24 hours to melt all ice. Place towels to catch water. Do not use sharp tools or heat guns on the evaporator.
• Access defrost components: Remove interior shelves and the rear panel to expose the evaporator. Identify the defrost heater (usually a tube or wire element at the base of the evaporator) and the defrost sensor clipped to the coil.
• Test the defrost sensor: Disconnect the sensor and measure resistance at a known temperature (e.g., room temperature). Compare to expected NTC values. If open or shorted, replace the sensor.
• Test the defrost heater: With the unit unplugged, disconnect the heater leads and measure resistance. A typical heater will show a finite resistance (e.g., 50–300 Ω). An open circuit indicates a failed heater that must be replaced.
• Inspect wiring and connectors: Check for burnt connectors, brittle insulation, or loose plugs between the heater, sensor, and control PCB.
• Evaluate the control PCB: If both heater and sensor test good, the defrost relay or triac on the main control PCB may be faulty. This requires PCB replacement, which should be performed by a qualified technician.

Note: Persistent E4 after component replacement suggests a control board issue or incorrect part specification; verify part numbers against the SMEG model label.