Display shows E4 and the refrigerator intermittently stops cooling or shows defrost issues.

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

Steps:

• Access the evaporator: Remove freezer drawers and rear panel to expose the evaporator and defrost heater (usually a metal or glass-encased element at the base or woven through the coil).
• Visual check: Look for burnt spots, broken heater sheath, or melted connectors.
• Test heater resistance: Disconnect heater leads and measure resistance with a multimeter. Typical values are between 50–300 Ω depending on model. An open circuit indicates a failed heater.
• Inspect connectors and wiring: Check for heat damage or corrosion at the heater terminals and along the harness back to the cabinet.
• Replace heater if faulty: Install a compatible Neff defrost heater, ensuring correct routing and secure mounting to the evaporator.
• Check PCB defrost relay (advanced): If the heater tests good but E4 persists and the evaporator ices up, the defrost relay or triac on the main PCB may be defective. This typically requires PCB replacement by a technician.