Diagnosis
F1 is a temperature sensor fault. The sensor (a thermistor) in the heating chamber is either disconnected, failed, or reading an impossible temperature.
How to Fix It
Unplug and let it cool. Remove the basket. Look at the top of the cooking chamber, near the back. You'll see a small silver probe. Ensure it's not bent and that no food is touching it. Clean it gently with a dry cloth. Plug it back in. The error may clear.
If That Didn't Work
The sensor's wire connection may be loose or burnt. This requires disassembling the main housing to check the connection at the control board. This is not a user repair. The sensor assembly must be replaced.
Heads Up
Do not attempt to bypass the sensor. The unit will not heat as a safety precaution. An open-circuit sensor is a common failure point on this model.