A pool pump hums and does not start
A hum with no shaft rotation is the motor, the start capacitor, or a seized pump. Turn the breaker off. It is a different fault from a pump that is already spinning and has lost prime.
· 5 min read
Turn the power off and leave it off. A motor that hums and sits there overheats.
A hum is not lost prime
Lost prime looks like a motor that is already spinning, with air in the lid and weak returns. A hum is the motor trying to turn and failing. The shaft does not spin, or it moves a fraction and stops. If the shaft is turning and the pot is full of air, start with why a pool pump loses prime.
Turn the breaker off. A humming motor left on power cooks the windings. Do not keep resetting the breaker to try it again.
What you can check with the power off
With the breaker off, try to turn the motor shaft the way that motor's manual describes. If it will not budge, the impeller may be clogged or the bearings may be seized. That is a wet-end or a motor job, matched to the plate.
If the shaft turns freely by hand and the motor only hums when power is applied, the start capacitor is a common cause on a single-speed motor. Replacing it means the power stays locked out, the capacitor rating matches the motor, and you can discharge the old one. If that is not you, stop and call a service tech. Do not guess a capacitor from a photo.
Match the motor from the plate
The useful lines are brand, horsepower, voltage, frame, service factor, and the pump model the motor is bolted to. Two 1.5 horsepower motors can have different frames and different shafts. The walk-through is in how to match a replacement part.
Pump motors are in equipment. On a variable-speed pump the drive and the motor are a pair. Replacing one without the model from the plate is how people buy a motor that bolts up and still will not run.
Questions
Why does my pool pump hum but not turn?
The motor is getting power and the shaft is not starting. Usual causes are a failed start capacitor, a seized bearing, or an impeller packed with debris. Turn the breaker off and leave it off.
Can I replace a pool pump capacitor myself?
Only with the breaker off, a capacitor whose rating matches the old part and the motor plate, and a way to discharge the old capacitor. Otherwise it is a service call. The wrong capacitor leaves the motor humming again.
What numbers do I need to order a replacement pump motor?
Horsepower, voltage, frame, service factor, and the pump model on the equipment plate. A horsepower number alone is not a match. Photograph the plate before you unbolt the motor.