My Hayward Vac seems to be sucking in air. I have a dedicated vac line and a jandy valve that can be set to skimmer, vac or somewhere in between. When the pool vac is plugged into the dedicated vac line and the valve is set to all vac/skimmer off the pump basket fills up with about half air and pressure drops from 10 psi to 5 psi. When I turn the valve to vac off/all skimmer the basket fills back up with water and the psi goes back up from 5 to 10. I wanted to make sure it wasn't the vac line itself so I hooked the vac up to the skimmer and had the same problem. Does this mean my Vac has gone bad? Is there a part that needs replacing?