Error Code E01 (or E21) indicates an open circuit in the temperature monitor.
Fix: Unplug the air fryer. Allow it to cool completely for at least 30 minutes. Plug it back in and see if the error clears. If the error code reappears, do not attempt further use or repair yourself.
If that didn't work: An E02/E22 error means a short circuit in the temperature monitor. For both E01/E21 and E02/E22, the resolution is the same if the error persists: Contact Cosori Customer Support. The unit requires service.
Heads up: If you ever see dark smoke, unplug immediately. Dark smoke points to burning food or a circuit problem. If it wasn't burnt food, that's another scenario requiring support.