Why Won't My Dishwasher Drain?

What it usually looks like

• An inch or more of dirty water sits in the tub after the cycle ends
• Water spurts out of the chrome air gap on the counter when the dishwasher drains
• The kitchen sink fills or gurgles while the dishwasher is running
• The dishwasher was just installed, or a new disposal was just put in, and it has never drained right
• A sour smell from the dishwasher between uses
• You hear the drain pump run but the water level does not drop

Likely causes, most common first

1. The disposal knockout plug is still in place

   A new garbage disposal ships with a plastic plug inside the dishwasher inlet. If the installer did not punch it out, the hose connects to a sealed port and the dishwasher cannot drain at all. If the dishwasher stopped draining the same day a disposal was replaced, this is almost certainly it.

2. Clogged or kinked drain hose

   The hose runs from the dishwasher to the disposal or sink tailpiece. Food sludge and grease build up at the connection, and a hose shoved into the cabinet can kink behind the machine. A hose with no high loop under the counter also lets sink water flow back into the dishwasher.

3. Blocked air gap

   Washington requires an air gap on dishwasher drains, which is the small chrome cylinder on the sink deck. Debris collects inside it. When it blocks, the dishwasher pushes water out the top of the air gap instead of into the drain. Pull the cap and clean it.

4. A slow or clogged kitchen sink drain

   The dishwasher drains into the same trap and branch line as the sink. If that line is partly packed with grease, the sink may seem fine while the dishwasher's fast discharge overwhelms it. The sink gurgling during the drain cycle is the clue.

5. Dirty dishwasher filter or failed drain pump

   Most modern dishwashers have a removable filter in the floor of the tub that catches food. When it is packed, the pump cannot move water. A pump that hums without moving water, or does not run at all, has a jammed impeller or a failed motor. Those are appliance repairs.

6. Check valve or drain solenoid stuck

   Some machines use a small flapper or solenoid in the drain path. If it sticks closed, nothing leaves the tub. Not a plumbing fault, but we can tell you that is what you are dealing with.

Safe things to check yourself first

• Run the kitchen sink for a minute. If the sink is slow or gurgles, the drain line is the problem, not the dishwasher.
• Pull the cap off the air gap and clean out any gunk with a bottle brush or by running water through it.
• Open the cabinet under the sink and follow the drain hose. Straighten any kinks and confirm it rises in a high loop before dropping to the disposal or tailpiece.
• If a disposal was recently installed, disconnect the dishwasher hose from the disposal with the power off and look into the inlet for the plastic knockout plug.
• Remove the filter in the bottom of the dishwasher tub, rinse it, and clear any debris around the drain impeller cover.
• Run a short cycle and listen for the drain pump. A hum with no water movement suggests a jammed pump.

How we diagnose and fix it

• Isolate the problem by testing the sink drain, the air gap and the hose path before touching the appliance, so you are not paying an appliance tech for a plumbing clog or the reverse.
• Punch out the disposal knockout, replace a crushed or sludge-packed drain hose, and secure a proper high loop or air gap connection.
• Cable the kitchen branch line from the trap arm or a cleanout when grease is the issue, and run water to prove it carries full flow.
• Rebuild a tailpiece or trap that has corroded or was assembled without a dishwasher branch, which we see in older kitchens where a dishwasher was added later.
• Replace a leaking or seized disposal when it is the one blocking the dishwasher drain.
• Tell you plainly when the fault is the dishwasher's pump, filter or control and refer you to an appliance repair service rather than charging to guess.

Questions people ask