Dishwasher Not Draining? Check These Causes in Order

Run your kitchen sink and disposal before you touch the dishwasher. If the sink drains slowly or gurgles too, the clog sits downstream of the appliance and no dishwasher part will fix it. If the sink runs fine and only the tub holds water, work through the checks below in order, from free and quick to a few hundred dollars.

Check the Filter and Sump First

Pull and clean the filter and sump first, because a clog there is one of the most common causes and fixing it costs nothing. Bail out the standing water with a cup and sponge, then remove the lower rack. Twist out the cylindrical filter at the bottom of the tub (the style varies, so check your manual) and lift out any flat screen under it.

Rinse the pieces under warm water with a soft brush. Then look into the sump, the shallow well the filter sits in, for broken glass, toothpicks, fruit pits, label scraps, and gritty sludge. That's how you clean a dishwasher drain filter, and it takes about ten minutes. Seat it fully when you put it back. A loose one causes its own problems. Your manual will say how often to repeat the job.

Is the Air Gap Clogged?

If your sink has an air gap, a small cylinder on the deck beside the faucet, a clog in it can stop drain water from leaving the dishwasher. Not every home has one. Many areas use a high loop instead, where the drain hose rises to the underside of the countertop before dropping to the drain, and local plumbing code decides which you need.

Pull off the chrome cap and the plastic cover beneath it. Clear the sludge with a bottle brush or a toothpick, then flush it with warm water. If water spits out of the air gap while the dishwasher runs, the blockage is farther down, in the disposal or the drain line.

How Do You Check the Drain Hose?

Trace the ribbed drain hose from the dishwasher to the disposal or sink drain, and look for kinks, sags, and clogs. Open the cabinet under the sink and watch for sharp bends, low spots where water can sit, and a hose crushed against the cabinet wall.

To test for a clog, loosen the hose clamp with a screwdriver or pliers and pull the hose off the disposal inlet or sink tailpiece. Point it into a bucket and run water through it, or blow through it. Slimy buildup or resistance means it's blocked. A replacement hose typically runs $15 to $40. Reconnect it with a snug drain hose clamp and keep the high loop intact.

If the kink is behind the dishwasher, you'll have to slide the unit out. Shut off the power and the water supply first, and only do it if you're comfortable with the connections.

Is the Garbage Disposal Knockout Plug Still In?

If the dishwasher never drained properly after a new disposal went in, a garbage disposal knockout plug left in the dishwasher inlet is the likely culprit. New disposals ship with a thin plastic plug sealing that port until someone connects a dishwasher. Skip the step and the water has nowhere to go.

Turn off the disposal's breaker, disconnect the drain hose from the inlet nipple, and shine a flashlight inside. If you see a solid disc, tap it loose with a screwdriver and hammer, then fish every piece out of the disposal chamber with pliers. Leftover fragments will jam the grinder. Keep your hand out of the disposal unless the power is off at the breaker.

How Do You Test the Drain Pump?

The drain pump sits beneath the sump and pushes water out, and if it's jammed or dead you'll hear either a hum with no flow or nothing at all. With the filter out and the power off, look for debris wedged around the pump inlet. On some models you can turn the impeller by hand. It should move with light resistance, and grinding or locking usually means glass or a seed is stuck in it.

A humming pump that won't move water is typically jammed or has a seized motor. A silent one could mean a dead motor, a loose wire, or a control board that isn't sending power. A replacement drain pump generally costs $40 to $150 for the part, and many models swap out with a nut driver in an hour or so. You'll need the model number from the label on the door edge to order the right one.

When Is It the Solenoid, Timer, or Control Board?

A faulty drain valve solenoid, timer, or electronic control board can look just like a bad pump, so check them only after the filter, hose, plug, and pump are cleared. Older machines often use a mechanical timer and solenoid. Newer ones rely on a control board that may flash an error code, so look the code up in your manual first.

Try a simple reset: switch off the breaker for five minutes, restore power, and run a drain cycle. Testing a solenoid or board properly takes a multimeter and a wiring diagram for your exact model. We'd stop here and call a pro rather than spend $100 to $350 on a control board on a hunch.

When Should You Call a Professional?

Call a pro when cleaning the filter, air gap, and hose doesn't help and the problem points to wiring, the control board, or the main drain line. Specific signs:

• An error code that returns after you've cleaned everything and reset the power.
• A breaker that trips when the dishwasher runs.
• A burning smell, or a pump that hums loudly and moves no water after you've cleared the sump.
• Water backing up in the sink, tub, or washing machine drain, which calls for a plumber rather than an appliance tech.
• Leaks around the base or door after you've disturbed connections.

What Does a Dishwasher Drain Repair Cost?

Drain fixes run from $0 for a cleaned filter to a few hundred dollars for a pro-installed control board, and local labor rates and your model drive the spread. These are typical U.S. ranges, not quotes.

A common rule of thumb says to replace rather than repair when the unit is roughly a decade old and the fix would cost around half the price of a new one. If you go that route, the ENERGY STAR site is a good place to compare efficient models. You can also search the Consumer Product Safety Commission for recalls on your current unit.

Tonight, run the sink test, then pull the filter and see what's sitting in the sump. That alone fixes more of these problems than any part you could order.