Pool pump electrical diagnostic on a daylight pad

How to Diagnose a Pool Pump That Won't Start

You flip the breaker on your pool pump and nothing happens — no hum, no click, no spin. A pump that won’t start has a much smaller set of likely causes than one that hums-but-won’t-spin. Here’s the diagnostic flow.

Symptom: complete silence

No noise from the motor at all means power is not reaching the motor windings. Check these in order:

1. Verify the breaker is actually on

Sounds obvious, but a tripped breaker is the #1 cause. Flip it firmly OFF and then back ON. If it trips again immediately, the motor or wiring has a fault — do not keep resetting it.

2. Verify the timer (if you have one)

Mechanical Intermatic timers can stick. Manually advance the dial to confirm the pump receives power in the current position. Digital and smart timers can lose programming — check the schedule and force a manual override.

3. Check the GFCI

Pool pumps are required to be on GFCI-protected circuits. A tripped GFCI looks like a tripped breaker but trips for ground-fault reasons (water intrusion, motor winding leak). Reset the GFCI. If it trips again immediately, the motor likely has an internal short and needs replacement.

4. Test voltage at the motor

If you have a multimeter, measure voltage at the motor’s power terminals with the breaker on. You should see 115V or 230V depending on motor wiring. No voltage = wiring problem. Voltage present but motor doesn’t spin = motor failure.

5. Pump locked rotor

Some motors have a thermal cutout that locks the motor off if it overheated. If your pump tripped on heat earlier, it may take 30–60 minutes to reset before it’ll start again.

Symptom: humming but not spinning

Different problem entirely. See our capacitor guide. A humming-but-not-spinning pump is almost always a failed start capacitor.

Symptom: starts, then immediately trips the breaker

Internal short in the motor windings or a damaged power cord. Both are serious electrical issues — do not keep resetting. Replace the motor or the cable.

Parts you may need

Jandy 25 MFD pump motor capacitor

Jandy 25 MFD Run Capacitor

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A.O. Smith Century 1.5 HP motor replacement

Century 1.5 HP Replacement Motor

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Heater fireman switch

Fireman Switch Kit

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If the breaker keeps tripping immediately: stop. A repeatedly tripping breaker often signals an electrical fault that can become a shock hazard. Call an electrician before doing further diagnostics yourself.

If you’ve worked through this list and still can’t start the pump, send PST Pool Supplies a photo of the motor data plate and the breaker panel. We’ll help narrow down whether you need a capacitor, a motor, or an electrician.

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