Air leaks are the usual suspect.

Yes, you almost certainly have an air leak on the suction side of the pump. Pool pumps don’t just lose prime for no reason — air is getting in somewhere.

Start with the easy stuff: the pump lid O-ring. Take it off, clean it, lubricate it with silicone pool lube, and reseat it. Make sure the lid is tightened evenly, not torqued down like a jar lid. If the O-ring is cracked or flattened, replace it.

Next check the drain plugs on the pump housing. They can vibrate loose or the O-rings fail. Also check any threaded fittings on the suction side — pump inlet, check valve, valves. A tiny hairline crack or loose union will suck air.

If the pump is below the water line (like in-ground), you can run a garden hose over each fitting while the pump is running. If the pump primes and holds, you found your leak.

Quick things to rule out: low water level in the pool (skimmer sucking air), a stuck weir door, or a clogged skimmer basket. But if your water level is fine and the basket is clean, it’s a leak.

Start with the O-ring. Nine times out of ten, that’s it.