Dishwasher Not Draining. Professional Troubleshooting Guide

Dishwasher Not Draining. A Professional Troubleshooting Guide

When your dishwasher leaves standing water at the bottom after a cycle, there's an issue with the drainage system. This is one of the most common problems we see in the field, and it should never be ignored. Leftover water creates odor, speeds up mineral buildup, and can lead to pump or control board failure. In this guide, you'll find out what causes this problem, how to check it yourself, and when it’s time to call a technician.

Main Reasons Your Dishwasher Isn't Draining

Clogged filter or drain path: Food debris, grease, and small particles build up in the filter and channels under it. Even if the filter looks clean on the surface, there can be a blockage deeper inside that prevents water from moving through the pump.

Blocked or misrouted drain hose: If the hose is kinked, clogged, or installed incorrectly, water won't drain properly. In new installations, one common mistake is leaving the disposal knockout plug in place, which blocks water flow entirely.

Faulty drain pump: If the pump makes a humming sound but doesn’t drain, its impeller might be jammed by glass, bones, or debris. If there’s no sound at all, the motor could be burned out or not receiving power.

Control board or timer issue: Sometimes the dishwasher doesn’t send the command to drain. This is often a logic or timing error on the main control board. The machine appears stuck and does nothing, even though it's finished washing.

Stuck float switch: A float switch stuck in the high position tells the dishwasher that there’s too much water in the chamber, preventing it from draining. It doesn’t trigger an error but blocks the next cycle step.

Clogged air gap or sink connection: If your dishwasher has an air gap near the sink, it can become blocked with grease or residue. A clogged sink trap can also block water from exiting, even if the pump is working.

Related Issues With Similar Symptoms

Some problems show the same signs as poor drainage but are actually caused by different components.

Door latch failure: If the door isn’t fully latched, the machine won’t enter or complete the drain cycle, even though it appears to be running.

Program freeze or cycle hang: A stuck cycle or logic error in the board may leave water standing without engaging the pump.

Drain solenoid failure: Some dishwashers use a solenoid valve to open the drain path. If the solenoid fails, the pump may run but water stays inside.

How to Diagnose the Problem Yourself

Important: Always disconnect the power before inspecting any internal parts. Never work inside a wet appliance while it's plugged in.

• 1. Remove the lower rack and filter. Rinse the filter thoroughly and check the cavity underneath for buildup.
• 2. Inspect the drain port for food bits, broken glass, or small objects.
• 3. Check the drain hose. Make sure it isn’t bent, squeezed, or clogged. It should loop properly to the sink or disposal.
• 4. If your unit has an air gap, twist off the cap and remove any visible residue inside.
• 5. Reconnect power and run a short cycle. Listen at the end the pump should activate with a noticeable sound. If you hear only humming or nothing at all, the issue is likely internal.

What You Can Fix Without a Technician

• Cleaning the filter and surrounding channels under the spray arm
• Flushing or replacing the drain hose
• Clearing a blocked air gap
• Removing the disposal plug (if recently installed)

In many cases, these actions are enough to restore drainage without tools or parts.

When to Call a Professional

If you’ve already checked the filter, hose, and air gap and water is still pooling, the problem is likely beyond surface level:

• The drain pump isn’t receiving power or has failed internally
• The control board isn’t sending signals to initiate the drain cycle
• There’s a short or break in wiring or sensors
• The drain solenoid or valve is stuck closed

If the problem comes back shortly after cleaning or happens intermittently, it likely points to a failing part that needs professional replacement. Quick diagnosis prevents further damage to your appliance.

What a Technician Does to Fix It

An experienced technician starts with a complete inspection checking filters, hoses, the drain pump, wiring, and the control system. Depending on the issue, the service may include:

• Unblocking or replacing the pump
• Resetting or repairing the control board
• Checking voltage and continuity to sensors and switches
• Testing full operation after repair

Most repairs can be done on-site without removing the dishwasher. In typical cases, the job takes under an hour.