Pool pump leaking water: the shaft seal
Updated : · Piscines VP
A leak between the pump and the motor almost always comes from the mechanical shaft seal. Replace it quickly: water runs into the motor's front bearing, which rusts and then squeals. A leak at the fittings or lid is often fixed by tightening or replacing an O-ring.
A puddle under the pump is never something to ignore. Where the leak is tells you everything.
Where is the leak?
| Location | Likely cause | Severity |
|---|---|---|
| Between pump and motor | Worn mechanical shaft seal | High |
| At the strainer lid | Dry, cracked or dirty O-ring | Low |
| At the fittings (unions, adapters) | O-ring, poorly sealed threads, cracked fitting | Medium |
| At the drain plug | Worn gasket, loose plug | Low |
| On the pump housing | Crack (often from freezing) | High |
Why the shaft seal is urgent
Water getting past the seal runs along the shaft straight into the motor’s front bearing. The bearing rusts, then squeals. A few weeks later it can seize and burn out the motor. See Worn bearings.
A seal costs far less than a motor.
In cold climates: watch out for frost
A pump left outdoors in winter with water inside can crack. That’s why it’s drained and stored somewhere warm at closing. See Reinstalling your pump in spring.
Piscines VP replaces shaft seals and motors in Laval and the Basses-Laurentides, Quebec.
Frequently asked questions
Can I replace the shaft seal myself?
It's possible for a handy person, but you have to take the pump apart, remove the impeller and install the seal without damaging it. A badly seated seal leaks right away. Many owners prefer a technician for this.
Why does the shaft seal wear out?
Age, running dry, very warm or chemically unbalanced water, and sand or debris passing through the pump.
Not sure of the cause? Take the 2-question diagnosis →
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