I guess the first step in solving this would be knowing the pump drive unit type. Up to 2012 the shafts were removable, they had a blue rubber bushing on each end and the shaft reached to the front propeller housing. Starting in 2012 the shaft was fixed on one side, it is not removable and stops at the top of the hole the impeller sits in. Non controllable models like the 6065 and 6085 persisted in the older design until late 2012, even early 2013.
In general this is caused by calcium build up on the shaft or a broken tip on the propellers, but it can vary slightly between the two designs. I would always start with making sure the propellers are undamaged, the ends hit stop tabs in the front cover to correct direction, if the ends are broke off, they can clear these tabs. If the shaft is fouled with calcium deposits, the propeller and magnet cannot freely slide back and forth to hit the tabs and correct direction, so this is also high on the list of things to check. If it is the old design, remove the shaft from the magnet and soak everything in 50/50 vinegar and water, the new design the shaft is part of the motor and the motor and drive unit need to be soaked.
