The reset is done to activate the counting system for the new filter(s) and cleaned pre-filter (the filter surface is part of the pre-filter). If your Philips Air Purifier features humidification, the appliance needs to be reset after descaling or replacing the humidification wick.
Your Philips Air Purifier or Humidifier is equipped with a filter replacement alert which warns you when the filter needs to be replaced. Most of Philips Air Purifiers are also equipped with a filter cleaning alert which warns you when the pre-filter needs to be cleaned. Please follow the filter clean and replacement instructions in the User Manual specific for your model.
If the above did not answer your question, please contact us.