Have a hot tub 2.5 years old one of the motors is 2 speed. When I push start on that one it just hums. Could it be just the capacitor. If so how can it be checked ?
Many single phase motors use a start capacitor. If it fails the motor can hum without starting. Sometimes they puff up and are obviously broke. If it appears OK visually then you will need to test it.
To test a capacitor you will need to disconnect it from the motor. If not use a digital multimeter set on resistance connected across the terminals of the capacitor. Initially it should read extremely low and the resistance should climb as the capacitor charges. Reversing your leads should yield the same result. If you get these results, the capacitor is good.
Otherwise a failed capacitor will read zero or infinite resistance.
If it is not the capacitor, it could be the pump motor is seized or the piping is plugged.
If you don't have a multimeter handly, you might be able to check the pump by turning it on and using a toilet plunger or perhaps a plastic soda bottle to push water through the return (in the tub) to get the motor to start turning. If the motor only starts going after giving it a push, then the capacitor is obviously the problem.