I've bought one returned the next day, replaced. Came home worked for two days same problem. both have the same trouble sensors. Call robot teck support, did soft reset, did not work. Called back, did hard reset. This requires removing the bottom and the battery. The battery must remain out for 5min. Replaced battery and bottom. Worked 2 minutes same Occurred Error 31. Text response was, looks like ive lost a coustomer... ya think