All air mattresses lose a little bit of air when being used.  When the NeverFlat pump detects that the air mattress has lost some air, the NeverFlat pump will turn on to refill the lost air.  When the NeverFlat pump is running this red light will be illuminated so that you know that the NeverFlat pump is working and filling up that lost air.  After the pump has filled up the air mattress the red light will go off until the next time the pump turns on.    If the light remains on for hours as well as the pump, and you are within the warranty period reach out to customer service for help here.