Westinghouse SP6390 Operation Manual page 16

2. When the ON / OFF Button and the Display screen are illuminated,
the red 'NCCO' Filter Installation Indicator flickers every 0.5 seconds
with 'Bi Bi' sound, user shall turn off unit and long press the ON / OFF
Button for 10 seconds until hearing a 'Da' sound. Then, press the Air
Speed Increase Indicator . 'nF' displays at Display Screen for
3 seconds indicating that the unit has exited the Reminding Mode.
User can turn on unit to operate it again.
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