E4 appears on the display and the air fryer stops heating or will not start a cooking cycle.

Safety first: Unplug the unit and allow it to cool completely. Work only when the fryer is cold.

Repair steps:

• 1. Access heater wiring: Remove basket and pan. Remove screws securing the top or bottom cover. Carefully separate the housing to expose the heater and wiring.
• 2. Locate thermal fuse: The thermal cutoff is usually wrapped in fiberglass sleeve and attached in series with the heating element leads. It may be clipped to the heater bracket.
• 3. Test continuity: Disconnect one lead of the thermal fuse and measure continuity with a multimeter. If it reads open (no continuity), it has blown and must be replaced.
• 4. Inspect wiring and connectors: Check for signs of overheating on the heater terminals, spade connectors, and wiring insulation. Replace any discolored or brittle connectors and wires with high-temperature rated parts.
• 5. Replace thermal fuse: Install a replacement thermal cutoff with the same temperature rating and current rating as the original Klarstein part. Crimp with high-temperature crimp sleeves; do not solder directly to the fuse body.
• 6. Investigate root cause: A blown fuse often indicates prior overheating. Verify that vents are clear, the fan is operating, and the NTC sensor is correctly positioned.
• 7. Reassemble and test: Refit covers, ensuring wiring is not pinched. Plug in and run a short test cycle. Confirm that E4 no longer appears and that the unit heats normally.

Warning: Never bypass the thermal fuse by shorting it; this removes critical fire protection.