DIAGNOSIS The laser particle sensor is likely dirty or obstructed. It's a small opening on the back of the unit. Dust, pet hair, or even direct airflow can fool it into reading high pollution.
FIX Power off and unplug. Use a can of compressed air to gently blast into the sensor opening on the rear panel. Follow up with a dry cotton swab to carefully wipe the outer rim. Avoid pushing debris in. Let it sit for a minute, then plug in. It should recalibrate in a few minutes in a clean environment.
IF THAT DIDN'T WORK The sensor needs a full reset cycle. Turn on the purifier and let it run in a known-clean room (like a bedroom with door closed) for at least 12 hours. The logic uses a running average, and it needs time to clear a false high reading.
HEADS UP Avoid placing the purifier directly under an HVAC vent, in a dusty corner, or within 3 feet of where people frequently sit—your breath contains CO2 and particles that can trigger the sensor.