DIAGNOSIS The sensor hasn't been manually reset to recognize the new filter. The unit tracks runtime, not actual dirt, and needs a reset with every filter change.
FIX Reset the filter indicator immediately. With the purifier ON, press and hold the Filter Reset button (the one with the circular arrow icon) on the control panel for 3-5 seconds until the filter status light turns from red back to green or blue.
IF THAT DIDN'T WORK Power cycle the unit. Unplug it from the wall for a full 60 seconds, then plug it back in and try the filter reset procedure again. This clears any temporary glitch in the indicator system.
HEADS UP The genuine Levoit filter has an RFID chip. If you installed a third-party or generic filter, the sensor may not read it correctly or at all, causing the alert to persist.