Display shows E3 and the refrigerator runs continuously or not at all.

Safety: Disconnect mains power before removing freezer panels or testing continuity.

Procedure:

• Access evaporator area: Empty the freezer, remove drawers and the rear interior panel to expose the evaporator coil and defrost components.
• Locate defrost sensor and fuse: On Neff NoFrost models, the defrost sensor and thermal fuse are usually clipped to the evaporator tubing or attached with a metal clip and heat-shrink tubing.
• Check for heavy ice build-up: If the evaporator is a solid block of ice, perform a full manual defrost (doors open, towels down) until all ice is gone. Do not chip ice away with sharp tools.
• Test the defrost sensor: Disconnect the sensor and measure its resistance at around 0–5°C (place the sensor tip in ice water). Compare the reading to the manufacturer's specifications; replace if open, shorted, or out of range.
• Test the thermal fuse: With the fuse disconnected, check for continuity. If it's open, it must be replaced; do not bypass it.
• Inspect wiring: Look for brittle or broken wires near the evaporator where they flex and freeze. Repair with proper insulated connectors and heat-shrink tubing.
• Reassemble and test: Replace any failed sensor or fuse with genuine Neff parts, reassemble the panel, restore power, and monitor operation. If E3 persists, the main PCB defrost circuit may be faulty and require professional replacement.