Error code E01 (or E21) indicates an open circuit in the temperature monitor.
Fix: Unplug the air fryer and allow it to cool completely for at least 30 minutes. Plug it back in and see if the error clears.
If that didn't work: The error requires service. Do not attempt to repair it yourself. Contact Cosori Customer Support. The same applies for error code E02/E22, which indicates a short circuit in the temperature monitor.
Heads up: If you see any other problems not listed in the troubleshooting guide, contact Customer Support directly.