Air fryer displays E4 and will not start a cooking cycle.

Safety first: Unplug the air fryer. Allow it to cool completely. Opening the cabinet exposes live parts when powered; keep it unplugged during all checks.

Steps to troubleshoot E4:

• 1. Confirm environment: Make sure the air fryer was not used under cabinets or in an enclosed space. Correct usage to prevent repeat overheating.
• 2. Access thermal fuse: Remove the rear or bottom cover to access the heating assembly. The thermal fuse is usually a small cylindrical or capsule-shaped component wired in series with the heater, often wrapped in heat-resistant sleeving.
• 3. Test the thermal fuse: Disconnect one lead and check continuity with a multimeter. If it reads open (no continuity), it has blown and must be replaced with the same temperature and current rating.
• 4. Inspect high-limit thermostat: Some Insignia models also have a resettable thermostat. Check for continuity; if open at room temperature and not resettable, replace it.
• 5. Check for root cause: Before replacing the fuse, inspect the heating element for signs of shorting to the chassis, and verify the fan is working properly. Also clean vents and internal grease buildup.
• 6. Replace thermal fuse: Install an OEM or equivalent Insignia-compatible thermal fuse. Crimp or solder connections using high-temperature-rated connectors and sleeving. Do not use regular electrical tape.
• 7. Reassemble and test: Reinstall covers, ensure no wires are pinched, then plug in and test. If E4 persists, the main control board may be misreading the safety circuit.

Warning: Never bypass a blown thermal fuse; doing so can create a serious fire hazard.