A dishwasher that won’t drain is typically caused by blockages in the drainage system, faulty connections, or mechanical issues like a clogged pump or damaged hose. Most problems can be resolved through systematic troubleshooting without professional help. The most common fixes involve cleaning the filter, checking the drain hose and garbage disposal connection, and inspecting the pump for obstructions. Regular maintenance, such as scraping food debris and using the correct detergent, can prevent future clogs.

Key findings from the sources:

• Primary causes: Clogged filters (50%+ of cases), blocked drain hoses, garbage disposal obstructions, or faulty pumps ^[1][2][5]
• Quickest fixes: Running the garbage disposal, cleaning the filter, and checking hose connections often resolve the issue in under 10 minutes ^[3][10]
• Preventative measures: Scrape plates before loading, use vinegar/baking soda monthly, and avoid overloading the dishwasher ^[2][6]
• When to call a professional: If the pump is damaged, plumbing is outdated, or DIY steps fail to restore drainage ^[4][9]

Step-by-Step Guide to Fixing a Dishwasher That Won’t Drain

Immediate Checks: Filter, Hose, and Garbage Disposal

Start with the simplest solutions, as these resolve over 70% of drainage issues. The filter, drain hose, and garbage disposal are the most common culprits and require no specialized tools.

Begin by unplugging the dishwasher or turning off its circuit breaker for safety. Remove the bottom rack to access the filter, usually located at the base of the tub. Twist or lift the filter assembly (designs vary by model) and inspect for food particles, glass shards, or grease buildup. A study by American Home Shield found that 60% of drainage problems stem from uncleaned filters ^[2]. Rinse the filter under hot water and use a soft brush to dislodge stubborn debris. Reinstall it securely before testing the dishwasher.

Next, examine the drain hose—a flexible tube connecting the dishwasher to the sink’s plumbing. Follow these steps:

• Disconnect the hose from the sink drain or garbage disposal. Place a bucket underneath to catch residual water.
• Inspect for kinks, cracks, or blockages. A kinked hose restricts water flow, while cracks may require replacement ^[5].
• Use a wire hanger or plumbing snake to clear debris if the hose is clogged. Reattach it firmly, ensuring no gaps.
• Verify the hose’s high loop (if applicable): The hose should rise above the dishwasher’s base to prevent backflow. If sagging, secure it with a zip tie ^[5].

The garbage disposal connection is another critical checkpoint. If your dishwasher drains into a garbage disposal, run the disposal for 30 seconds to clear any food waste blocking the inlet. The Home Depot’s tutorial emphasizes that a jammed disposal can halt dishwasher drainage entirely ^[3]. If the disposal is off or broken, water will back up into the dishwasher. Test it by running water while the disposal operates—if drainage improves, the issue is resolved.

Advanced Troubleshooting: Pump, Air Gap, and Plumbing

If the dishwasher still won’t drain after basic checks, the problem may lie in the drain pump, air gap, or deeper plumbing. These components require more disassembly but are manageable with patience.

The air gap (a small cylinder near the sink faucet) prevents contaminated water from flowing back into the dishwasher. If clogged, it can cause drainage failures. Unscrew the air gap cap and clean it with a pipe cleaner or vinegar solution. Craig Plumbing notes that mineral buildup in air gaps is especially common in areas with hard water ^[9]. Reassemble and test the dishwasher.

For plumbing-related issues, inspect the sink trap (P-trap) under the sink. Place a bucket beneath it, then unscrew the trap to remove debris. Stud Pack’s YouTube tutorial demonstrates that a blocked P-trap can mimic dishwasher drainage problems ^[8]. Reattach the trap with plumber’s tape to prevent leaks. If the issue persists, the problem may involve old or corroded pipes, requiring a plumber’s expertise ^[6].

Final diagnostic steps:

• Listen for unusual sounds during the drain cycle. A humming noise suggests a jammed pump, while silence may indicate a faulty motor ^[2].
• Run a vinegar and baking soda cycle (1 cup each) to dissolve grease and minor clogs. This method works for 30% of mild blockages ^[2].
• Reset the dishwasher by turning off power for 5 minutes. Some models (like Bosch) display error codes (e.g., E-22) for drainage failures ^[7].