U.S. Motors pool pump hums but will not start; motor housing gets warm and trips the breaker or thermal overload.

Safety first: Turn off power at the breaker and verify no voltage is present. Capacitors can hold a charge; discharge them safely before handling.

• Check shaft rotation: With power off, remove the rear motor cover or use the shaft end to turn the motor shaft by hand. If it spins freely, the issue is likely electrical (capacitor/start circuit).
• Inspect and test capacitor: Locate the start capacitor on the U.S. Motors motor (usually under a metal or plastic cover). Remove it and test with a capacitance meter. Replace if the value is out of tolerance or if the capacitor is bulged or leaking.
• Check start switch/relay: On motors with a centrifugal switch, inspect contacts for burning or sticking. Clean or replace the switch assembly if it does not open/close properly.
• Verify voltage under start: Use a meter to confirm that line voltage remains stable when the motor attempts to start. Significant drop indicates supply issues.
• Reassemble and test: After replacing the capacitor or switch, reassemble all covers, restore power, and test the pump. If it still only hums, the start winding may be damaged and the motor should be replaced.