Check the pump lid O-ring first.

Most likely an air leak on the suction side — and the pump lid O-ring is the most common culprit.

Start with the easy stuff. Turn the pump off, open the lid, pull the O-ring out, and clean the groove. Look for cracks, flat spots, or grit. If it looks tired, replace it. A thin coat of silicone lubricant (pool-specific, not petroleum) on a new or cleaned O-ring helps it seal.

While you’re at it, check the water level in the pool — if it’s below the skimmer, you’re sucking air. Also make sure the skimmer basket and pump basket are clear and the lid is tightened hand-tight (don’t wrench it). A loose union or valve on the suction side can also let air in.

If those don’t fix it, you might have a small leak in the underground pipe, but that’s less common. Try the free stuff first.

A few minutes of maintenance now saves you an afternoon of bleeding air.