Oster air fryer displays E4 and will not start or stops mid-cycle with a beep.

Safety: Unplug the air fryer. Do not bypass safety devices such as thermal fuses or thermostats; they prevent fires.

E4 is often associated with the high-limit safety circuit detecting a fault.

• Allow full cool-down: Let the unit sit unplugged for at least 30 minutes. Some thermostats auto-reset when cooled.
• Check for blockage: Confirm that air inlets and outlets are not blocked and that the unit is not used under cabinets where heat accumulates.
• Access heater circuit (advanced): Remove the rear/bottom cover to expose the heating element wiring. Locate the thermal fuse and high-limit thermostat (usually small disc or inline component attached to the heater bracket).
• Test continuity: With a multimeter, check continuity across the thermal fuse and thermostat. An open reading indicates a failed component.
• Replace failed safety device: If the thermal fuse or thermostat is open, replace it with an Oster-specified part of the same temperature and current rating. Do not substitute random fuses or bypass the device.
• Inspect wiring and terminals: Tighten any loose spade connectors on the heating element and safety devices. Look for discoloration or melting that indicates overheating.
• Control board check: If all safety devices test good but E4 persists, the main control board's overheat detection circuit may be faulty and require replacement.