The color of the degree symbol (on the display panel) changes from white to red to indicate that it’s time to wash/change your filters. When you’re done, just hold down the filter button on the unit for 5 seconds until it beeps and resets.
To learn more about cleaning and replacing your filters, visit:
https://windmillair.com/support/#reamaze#0#/kb/product/how-do-i-clean-the-filter