DIAGNOSIS You likely didn't fully reset the filter timer after installing the new filter. The timer is independent of the physical filter; if you don't reset it, it continues counting down from the old remaining time.
FIX Perform a filter reset now. With the unit on, press and hold the Filter Reset button for 3-5 seconds until the indicator light turns off. This sets the timer back to zero (approx. 6-8 months of runtime). The light should not reappear for a long time.
IF THAT DIDN'T WORK Ensure you purchased a genuine Levoit replacement filter designed for the Vital 100/100S series. Some third-party filters lack the correct RFID tag or physical dimensions, which can confuse the system.
HEADS UP The filter reset button is also used to confirm a new filter is installed. Always reset immediately after any filter change, even if the light isn't on yet, to sync the timer.