Lower the skimmer flap if it is stuck in an upright position.
Add water to the pool if the water level is too low, causing the skimmer intakes to suck in air.
Clean the skimmer basket if it is full of leaves or other debris. Clogged skimmers can block water from exiting, allowing air to enter the return lines.
Turn off the pump. Examine the pump hardware. Look for spouts of water emerging from connections and fittings. If you find one, it is the source of the air leak. Some common locations for leaks are threaded adapters or other devices that screw into the pump. The vibration of the pump loosens them over time.
Fix any leaks you find by unscrewing the adapter or device, then replacing the Teflon tape that is around the threads. Pull off the old tape completely. Wrap the fresh piece of tape around the threads. Allow the tape to overlap itself halfway with each successive wrap. Cut the tape so that there is no overhang that could interfere with the water flow. Finally, re-attach the adapter or device. Screw it in firmly, but do not overtighten.
Check all rubber gaskets (often called “O-rings”) for cracking or decay. Replace them if necessary. Depending on your pump, there may be O-rings in the valves inside the pump housing as well as on the outside connection ports. Also, there may be an O-ring in between the pump lid and the outside of the pump. Pumps with Jandy valves have two O-rings: one in the cap and the other in the shaft of the valve.
Check the drain plugs. Consult your owner’s manual for their exact location. Typically, they are on the main body of the pump. If the drain plugs are threaded, repair them by replacing the Teflon tape. If they have cracked O-rings, replace them.
Contact a pool-repair service if the air still appears in the water jets. The problem may be the pump machinery itself. For example, there may be a leak in the mechanical seal where the motor shaft connects with the pump. These repairs usually require a replacement part and a professional’s knowledge.