DIAGNOSIS ERR is a general sensor error. On the Vortex Plus, it most often relates to the temperature sensor detecting a problem during the heat-up cycle, like it's taking too long to reach temperature or the reading is way off.
FIX 1) Unplug the air fryer and let it cool down completely for at least 30 minutes. This resets the internal computer. 2) Plug it back in. Before you start cooking, make sure the basket and interior pan are correctly installed and the fryer is on a stable, heat-resistant surface with several inches of clearance on all sides. Poor ventilation can cause overheating and trigger this error. 3) Try a simple cook function like 350°F for 5 minutes to see if it happens again.
IF THAT DIDN'T WORK The temperature sensor itself might be faulty or have a loose connection. This isn't a user-serviceable part. If the error persists after a full cool-down and with proper ventilation, you'll need to contact Instant Brands support for warranty service or a replacement.
HEADS UP An 'ERR' that flashes and then the unit turns off is different from the 'FOOD' prompt. Don't ignore a recurring ERR, as it indicates the fryer can't regulate its temperature safely.