Problem Summary
The pump loses suction repeatedly, requiring re-priming, or runs with visible air in the pump basket/pot.
A pump that repeatedly loses prime is drawing air into the suction side of the system somewhere, and the fix depends on exactly where the air is entering.
Possible Causes
Air leak on the suction side of the plumbing
Any fitting, o-ring, or union between the pool and the pump that isn't fully sealed can pull in air under suction, even if it wouldn't leak water under pressure.
Water level in the pool too low relative to the skimmer
If the water level drops below the skimmer's effective intake range, the skimmer draws air along with water.
Worn pump lid o-ring or a loose pump lid
The pump lid is a common, easy-to-check air-entry point that's often overlooked.
Diagnostic Steps
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Check pool water level relative to the skimmer opening first, since it's the simplest thing to rule out.
Low water level alone can fully explain intermittent air intake.
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Inspect the pump lid o-ring and all visible suction-side unions for wear or looseness.
A visibly dry, cracked, or loose o-ring/union is a likely entry point.
Solutions
Restore the pool's water level and re-prime the pump
Addresses cause: Low water level
Top up the pool so the skimmer draws water only, then re-prime the pump per its normal procedure.
Replace worn pump lid o-ring / tighten unions
Addresses cause: Worn o-ring or loose fitting
A new o-ring and properly tightened (not over-tightened) unions resolve most suction-side air leaks.
When to Contact a Specialist
If the pump keeps losing prime after checking water level and the pump lid, the leak is likely underground or in a buried suction line, which needs a professional leak check rather than DIY troubleshooting.