Symptoms
- Loud hum from the motor with no movement
- Slight vibration but the pump doesn't turn
- Circuit breaker trips shortly after the hum starts
- Motor smells hot after humming for a while
Likely causes
- CommonPump seized or jammed internallyIf the pump can't turn, the motor will hum against the resistance rather than spin.
- CommonFailed start capacitorMany electric motors need a capacitor to get spinning initially; a bad one leaves the motor unable to start under load.
- PossibleWorn motor bearingsBearings seizing or badly worn can prevent the shaft from turning freely.
- PossibleThe unit has been sitting unused for a long timePumps and seals can stick after long periods without use, especially if any moisture was left inside.
What to do
- Turn off and unplug the machine immediately; don't let it continue humming, since this can overheat and damage the motor windings.
- Try to manually rotate the pump shaft or motor fan (if accessible) by hand to see if it's physically stuck.
- If it was in long-term storage, try gently working the shaft back and forth by hand to break loose any minor stiction.
- Check for an obvious jam, like debris caught in the pump or fan area.
- If the shaft turns freely by hand but the motor still just hums when powered, a start capacitor is a likely cause on capacitor-start motors.
- Do not repeatedly try to power it on while humming, since this risks burning out the motor.
- If it's a seized pump or bad capacitor, a small appliance or power-equipment repair shop can test and replace the specific failed part.
Tools and parts
- None required for basic checks
Motor start capacitorSearch: “electric motor start capacitor replacement”
When to call a pro
A humming motor that won't turn under load is best diagnosed by an appliance or power-equipment repair shop, since it may need capacitor or bearing replacement.
Safety
Use caution
Unplug the unit immediately if the motor hums without turning; letting it continue can overheat and damage or burn out the motor.