Why won't water pump out of my dishwasher tub?

The drain may be clogged. If you have an air gap, clean it. Check to see if your kitchen sink is draining well—if not, you may need a plumber. If the dishwasher drains into a disposer, run the disposer clear. The air gap can be cleaned by lifting off the chrome cover and unscrewing the plastic cap to clean with a toothpick.