Freezer shows error code E4 and may not enter or exit defrost cycles correctly, causing either heavy ice or excessive warming during defrost.

Safety first: Disconnect power before testing heater or thermostat. Risk of electric shock.

• Inspect evaporator area: Remove internal rear panel to access the evaporator, heater, and thermostat.
• Test heater: Disconnect heater leads and measure resistance with a multimeter. An infinite reading indicates a failed heater that must be replaced.
• Check defrost thermostat/fuse: At freezer temperature, the thermostat or fuse should show continuity. If open, replace with the correct Ariston part.
• Examine wiring: Look for burnt connectors or damaged insulation along the heater circuit.

When to call a technician: If all components test good, the control board defrost relay may be defective and should be replaced by a professional.