What does 'Err' displayed on the LCD screen mean?

When 'Err' appears on the LCD display, it indicates a sensor fault. The alarm will give a fault warning within 3 minutes and repeat at least once per minute until the fault is corrected. Volatile gases like ethanol can temporarily affect the sensor; place the unit in clean air for 24 hours to recover. If it doesn't recover after 24 hours or shows permanent damage, do not use it further.