This is not usually a home handy person fix.
If the water doesn't drain from your dishwasher, check these:
Drain line/air gap
Drain valve and/or solenoid
A clog in the drain line or air gap (if there is one) is the usual reason that a dishwasher won't drain. Often the problem is at the point where the drain line attach's to the garbage disposer or household drain line. If you remove this line, you can clear any debris from the hose or hose connection. Be sure to reattach the hose before starting the dishwasher again.
Your dishwasher pump ejects the water. The pump is usually mounted directly to the motor, then attached to the bottom of the dishwasher. You can reach the pump from inside the dishwasher, but first you need to remove the lower rack, the spray arm, and the spray arm support.
Look for an impeller--a round plastic fan blade-type of device that spins around. This is the wash impeller, which forces the water through the spray arm. Beneath the wash impeller is the drain impeller, which is similar in size and shape to the wash impeller. The drain impeller pushes the water toward the drain port. These components make up the pump. If any of the pump components are defective, you need to replace them.
Drain valve and/or solenoid
Many dishwashers use a drain valve with an electric solenoid. When electricity flows to the solenoid, the valve opens and diverts the water to the drain. Sometimes the solenoid, or the diverting lever, sticks and prevents the dishwasher from draining or filling properly. Try to free up the solenoid to lubricate the lever. Otherwise, you may have to replace the solenoid or pump assembly. With these systems, the motor always rotates in one direction. When it's energized, the drain valve diverts the water.
Other dishwashers simply reverse the direction of the motor to drain the dishwasher. These units don't have a drain valve. Instead, there's a drain hose connected directly to the pump housing.
One brand of dishwasher uses a belt to drive the pump. If this belt is broken or has fallen off, replace it.
If the motor isn't turning or working, the unit won't drain. First check to be sure you have power to the dishwasher. If not, see the section "It doesn't work at all." If the motor hums but doesn't turn, it may need to be replaced.
Some dishwashers are susceptible to getting stuck if you don't run them regularly. If you haven't run the dishwasher for more than a week, you may need to manually spin the motor to free it up. If the motor is defective, you need to replace it. Dishwasher motors can't be serviced.
Part of what the timer does is control the motor and drain valve. If the timer doesn't work properly, the water may not drain and you need to replace the timer. This problem is uncommon.
Edited by Neilwill on 12/19/2009 at 12:43 AM EST