My Polaris 3900 is 5 years old. (Yes, hindsight is 20-20) Rebuild by company rep in the spring, new hose, new backup valve. Working so-so since, but just was out cleaning my pool and saw the Polaris goes to the wall and just sets there. Lifted it out and saw the two wheels on the right are turning, the left one dead. The thing just keeps getting stuck on a wall or stair and sitting there. Any advice would be appreciated.