DIAGNOSIS If the timer works but food is consistently undercooked, the unit is not reaching its set temperature. This is often a calibration issue, a failing heating element, or a blocked air intake.
FIX First, check for airflow blockages. Ensure the air fryer is on a hard, flat surface with at least 5 inches of space behind it where the vent is. Anything blocking the rear vent will cause overheating and the unit will cycle the element off, reducing average temperature. Run a test with an oven thermometer inside the empty basket at 350°F for 10 minutes to see the actual temperature.
IF THAT DIDN'T WORK The temperature sensor may be giving a false high reading, causing the element to cycle off prematurely. This is related to the F1 error but not severe enough to trigger it yet. There's no user calibration. This is a component failure requiring service.
HEADS UP All air fryers have temperature swings, but consistent undercooking by a large margin is a fault. Before concluding it's broken, verify you're not using frozen food without adding time and that you're preheating the unit for 3 minutes as recommended.