Any motor exposed to the elements can suffer from "flash rusting" inside the housing no matter how well it is sealed. If a motor hums instead of spinning on startup, try this simple procedure before replacing the motor.

After disconnecting the power, remove the plastic cover on the back of the motor.  Locate the shaft on the back of the motor and attempt to turn it clockwise with a flat head screwdriver. Continue to rotate the shaft until it turns easily. If the shaft does not spin, the motor is probably rusted tight and needs replacing. After breaking the shaft loose, replace the rear plastic cover and restore power to the motor, and it should take right off.

You can reduce issues with flash rusting by removing the jet pump unit from the cool cell system in the fall and storing it inside out of the weather. It is also important to remove the plug in the bottom of the pump housing to prevent damage from freezing. Installing a protective cover over the motor will help protect it from the elements during the cooling season.