Pentair front wheels not turning - Pentair White/Gray Legend Platinum Automatic Pool Cleaner - Ll105pm

Make sure that your pool cleaners back up valve is cycling properly. If it is not giving you the proper thrust, the wheels will not turn in unison. Also, if one of your wheels is showing excessive wear and tear, that will cause this problem and the wheel will need to be replaced. Make sure that your RPM is not too high (causing one of the wheels to leave the floor) or too low (so that the wheels do not turn properly).

You might want to pull the drive wheels and see if their might be a small pebel stuck in the drive gears on the wheel.