DIAGNOSIS Error 31 is a cliff sensor failure. One or more of the four infrared cliff sensors on the underside are either dirty or malfunctioning, causing the robot to think it's on a ledge.
FIX Power off the robot. Turn it over and clean all four black cliff sensor windows on the bottom with a dry microfiber cloth. Clean the bumper area around them. Remove any protective films. Place the robot on the floor and power it on.
IF THAT DIDN'T WORK The robot may need a hard reset to clear the error. Press and hold the CLEAN button for 20 seconds until all lights turn off. Release, then press it once to restart. If error 31 persists, the sensor array may be faulty and requires service.
HEADS UP This error is frequently triggered by dark floors or very high-pile rugs that absorb the infrared signal. The robot will not run with an active Error 31 for safety reasons.