Diagnosis
Error E1 is a temperature sensor fault. The NTC thermistor in the fry chamber is either disconnected, damaged, or giving a reading out of range.
How to Fix It
Unplug the unit and let it cool completely. Remove the basket. Look at the top rear wall of the fry chamber. You'll see a small metal probe. Check that its wire connector is secure. If it is, the sensor itself is likely bad. You need a replacement thermistor. Contact Cosori support for the part.
If That Didn't Work
The main control board could be misreading the sensor signal. That requires board replacement. Support will guide you through diagnostics.
Heads Up
Do not try to bypass this error. The unit will not heat to prevent a runaway overheat. Running it with E1 is unsafe.