Your Philips Air Purifier or Humidifier needs to be reset after each filter replacement. This is done to activate the counting system for the new filter(s).
Also, your Air Purifier/Humidifier is equipped with a filter replacement alert. It warns you when the filter needs to be cleaned (pre-filter only) and replaced.
If you do not reset the appliance after replacing a new filter, the appliance will alert you to replace a filter far too early for its actual life span. The filter replacement alert and reset filter lock features of the appliance ensure that filters are always at optimal condition so that you can breathe healthy air always.