DIAGNOSIS: The float sensor inside the dirty water tank is stuck in the "full" position, usually due to mineral scale or debris.
FIX: Remove the dirty water tank from the Clean Base. Open the tank's top flap. Locate the small white plastic float inside the tank cavity. Manually move it up and down several times. Rinse the entire tank with warm water, shaking it vigorously to dislodge any scale. Ensure the float moves freely.
IF THAT DIDN'T WORK: The sensor connector inside the Clean Base docking port may be corroded. Unplug the Clean Base. Use a dry cotton swab to clean the three metal contact pins in the dock where the tank sits. Let it dry completely.
HEADS UP: Never use bleach or harsh chemicals to clean the dirty water tank. It can damage the float sensor and leave fumes that trigger the robot's air quality sensor.