Getting your dishes sparkling clean is the whole point of a dishwasher. But when that appliance fails to do its job and leaves your dishes sitting in dirty water, it’s incredibly frustrating. A dishwasher that fails to drain properly can also lead to foul odors, leaks, water damage, and mold growth. So getting to the root of the problem and fixing it quickly is essential. In this comprehensive guide, we’ll explore the 10 most common reasons why your dishwasher isn’t draining properly. We’ll provide detailed explanations of each issue along with step-by-step instructions on how to diagnose and repair the problem yourself.
Overview of Dishwasher Drainage Systems
Before we dive into specific issues, let’s take a quick look at how dishwashers drain water. Understanding the basic components involved in drainage can help you troubleshoot problems.
Key Drainage System Components
- Drain hose: Flexible hose that carries dirty water out from the dishwasher tub to drain line or garbage disposal
- Drain pump: Motorized pump that pushes water through the drain system
- Air gap: Acts as a backflow preventer between drain hose and sink drain
- Drain valve: Opens and closes to control water flow out of tub
- Filters: Catches food debris from water before entering drain pump
Drainage Process
- Dirty wash water containing food soil and detergent fills the dishwasher tub during the wash cycle
- Water is pumped from the tub through various filters to remove food particles
- The drain valve then opens to allow the water to exit the tub
- Water flows out through the drain hose, then through air gap, before emptying down the sink drain line or into the garbage disposal
- The drain cycle repeats as needed until tub is empty
Now let’s look at 10 reasons why this drainage process can fail and how to get your dishwasher draining properly again.
10 Common Reasons a Dishwasher Won’t Drain
1. Clogged or Broken Drain Hose
The drain hose is the most likely culprit when a dishwasher fails to drain properly. A clog or crimp in this critical drain component is enough to stop water from exiting the appliance.
SYMPTOMS
- Standing water in the bottom of dishwasher
- Water overflowing out of dishwasher
- “Check water supply” error code
HOW TO FIX
- Turn off power to dishwasher at circuit breaker.
- Pull dishwasher out from under counter.
- Disconnect drain hose from sink drain or garbage disposal.
- Inspect drain hose for blockages or crimps.
- Clear out any debris, food, or hard water scale clogging hose.
- Straighten out any kinks and reinstall if hose is undamaged.
- If drain hose is cracked or worn out, replace it with new hose.
- Reconnect hose, push dishwasher back into place, test drainage.
2. Clogged Dishwasher Filters
Dishwasher filters are first in line to get clogged with food particles, grease, bone fragments, and other debris that washes off dirty dishes. When filters get excessively dirty, they’ll block water from properly draining from the tub.
SYMPTOMS
- Water pooling in bottom of tub
- Dishwasher won’t finish cycle
- Dishes left dirty with food still stuck on them
HOW TO FIX
- Remove the lower dish rack from dishwasher tub.
- Twist off the cylindrical fine filter located at the bottom center of the tub.
- Pull out the flat main filter from the back wall of the tub.
- Rinse both filters under the sink faucet to clear debris.
- Reinstall filters in proper order and orientation.
- Run dishwasher to verify full drainage.
TIP: Check and clean dishwasher filters monthly
3. Drain Pump Failure
The drain pump pushes out water from the tub through the drain system. If this motor fails, drainage problems result. Signs of a faulty drain pump include loud grinding noises, low water flow, and standing water in the bottom of the tub.
SYMPTOMS
- Water left standing in bottom of tub
- Loud grinding noise when drain cycle engaged
- Dishwasher won’t finish cycle
HOW TO FIX
- Turn off power to dishwasher.
- Remove lower dish rack and filters.
- Locate pump at front right corner of tub.
- Disconnect drain pump electrical wiring and water hoses.
- Unscrew pump mounting hardware and remove.
- Inspect pump impellor for debris or wear (replace if damaged).
- Reinstall pump with new rubber mounting gasket.
- Reattach hoses and wiring before reinstalling filters and rack.
TIP: Make sure hard objects don’t get jammed under pump impellor
4. Faulty Drain Valve
The drain valve is essentially the exit door for removing water from the dishwasher tub. When working correctly, this solenoid opens and closes on command to control drainage. If the valve or valve motor fails, it remains closed and prevents water from exiting.
SYMPTOMS
- Water won’t drain from tub
- Dishwasher stops mid cycle
- You’ll likely see an error code on display
HOW TO FIX
- Turn off power to dishwasher.
- Pull dishwasher out and lay on back.
- Locate control module at bottom corner of tub.
- Unplug drain valve electrical connector.
- Unscrew mounting screws and remove valve.
- Inspect valve interior for debris blocking plunger.
- Test voltage going to valve when drainage cycle activated.
- Replace valve if plunger sticks or voltage input faulty.
TIP: Avoid overloading dishwasher to prevent food debris in valve
5. Blocked Air Gap
The plastic air gap installs above the sink between the drain hose outlet and drain pipe. It prevents contamination risk if water attempts to flow back into dishwasher from sink. But when debris clogs this gap, proper drainage gets blocked.
SYMPTOMS
- Water pooling in bottom of tub
- Water bubbles up through air gap if completely blocked
HOW TO FIX
- Verify air gap components installed correctly.
- Shut off water supply valves to dishwasher.
- Use small brush to clear debris out of air gap inlet.
- Flush with tap water; replace entire air gap assembly if still clogged.
TIP: Routinely clean air gap device to maintain proper drainage
6. Kinked or Blocked Drain Line
If the dishwasher drain line (through the air gap) that leads to your sink drain gets kinked or clogged, drainage flow out of the dishwasher will be disrupted. Standing water in tub or even water overflowing onto floor can result.
SYMPTOMS
- Water overflowing out of dishwasher
- Standing water pooled in bottom of tub
HOW TO FIX
- Shut off water supply to dishwasher.
- Disconnect drain line from sink drain.
- Run water through drain line to flush debris.
- Straighten or replace if drain line is pinched.
- Reconnect drain line and verify no leaks.
TIP: Periodically inspect drain line condition under sink
7. Clogged Sink Drain Line
When the drain line carrying water out from the dishwasher air gap empties into a clogged sink drain, backpressure prevents proper drainage from occurring. Clearing sink clogs is required for dishwasher functionality.
SYMPTOMS
- Standing water in dishwasher tub
- Water overflow from air gap onto sink top
HOW TO FIX
- Shut off dishwasher and use bucket to catch water.
- Plunge sink drain with sink plunger to dislodge clogs.
- Remove pipes under sink to inspect and manually clear debris.
- Install inexpensive sink strainer basket to trap food scraps.
- Use enzymatic drain maintainer monthly to digest buildup.
TIP: Don’t pour grease, fat or coffee grounds down sink drains
8. Garbage Disposal Jam
Attaching the dishwasher drain line to the garbage disposal seems convenient. But when that grinding chamber jams with harder items like bones, glass, pennies, or popsicle sticks, the backpressure created can flood a dishwasher.
SYMPTOMS
- Water pools in dishwasher tub
- Foul odors come from garbage disposal
HOW TO FIX
- Shut off electrical power to garbage disposal.
- Rotate disposal blades manually from the bottom to check rotation.
- If jammed, use a special wrenchette tool to work the spinning mechanism free.
- Check and remove debris blocking the grinding ring.
- Press the reset button on disposal before testing.
TIP: Run plenty of cold water when running disposal
9. Bad Drain Pump Impeller
The drain pump uses a spinning impeller blade to sling water through the drain system. Over years of use, this important pump component can wear out and lose drainage effectiveness. Replacement restores normal functionality.
SYMPTOMS
- Water left standing in tub
- Loud grinding noise from pump area
HOW TO FIX
- Shut off dishwasher power at circuit breaker.
- Pull dishwasher out and lay carefully on back.
- Remove drain pump hoses and electrical connectors.
- Unscrew mounting screws and remove entire pump.
- Separate outer casing to inspect impeller blade condition.
- Replace defective impeller if worn, chipped, or broken.
TIP: Also replace old drain pump gaskets when installing new impeller
10. Malfunctioning Control Board
The control board is essentially the computer brain that oversees dishwasher functions like loading water, heating, washing, draining, etc. If this electronic component software gets corrupted, all cycles can fail to finish properly.
SYMPTOMS
- Dishwasher won’t start or finish cycles
- Error codes or unusual wash behavior
HOW TO FIX
- Turn off power and water supply to dishwasher.
- Remove outer control panel screws.
- Disconnect wiring and remove faulty control board.
- Install replacement control board.
- Test dishwasher functionality.
TIP: The control board should only be replaced once all of the other parts are verified.
When to Call a Repair Professional
As you’ve seen, many common dishwasher drainage problems can be fixed with some simple troubleshooting and DIY repairs. But not all malfunctions are easy homeowners fixes.
Call for professional dishwasher help if you encounter any of the following issues:
- Leaking water lines or components
- Damaged or hazardous electrical wiring
- Major tub leaks or overflow problems
- Strange burning smells or high heat levels
- Door alignment, latch or lock problems
- Mold or mildew buildup inside tub
Dishwasher repair technicians have specialized tools, testing capabilities, and parts sourcing expertise to properly diagnose and fix complex appliance issues.
They can also legally access dangerous electrical connections and water lines in your home to make necessary repairs. Attempting hazardous dishwasher system repairs without proper qualifications can risk electrocution, fires, flooding and void your appliance warranty coverage.
Preventing Future Dishwasher Drain Problems
Like other home appliances, some maintenance practices will keep your dishwasher functioning better for longer. Here are 6 tips to avoid needing dishwasher drainage repairs going forward:
1. Clean Filters Monthly
Don’t let debris clog your dishwasher filters. This quick monthly task keeps water flowing freely.
2. Use Dishwasher Cleaner Monthly
Special formulated cleaners break up grease and limescale buildup that can impede drainage.
3. Unclog Air Gap Regularly
Clear any debris blocking this water backflow prevention device.
4. Inspect & Straighten Drain Hose Yearly
Replace any cracked or worn out drain hoses. Keep hose as straight as possible without sharp bends.
5. Flush Inlet Water Lines Yearly
Detach supply lines and run water through to clear mineral deposits from hard water.
6. Deep Clean Dishwasher Annually
Remove all internal parts like racks, filters, arms. Scrub away grease and scale buildup for optimal drainage and washing.
Dishwasher Not Draining Diagnosis Chart
Use this dishwasher troubleshooting chart of common symptoms and likely root causes before starting repairs:
| Symptoms | Possible Cause | Solution Checklist |
| Large puddles of water in bottom of tub | 1. Clogged or kinked drain hose2. Clogged dishwasher filters 3. Blocked air gap device | 1. Inspect and unclog drain hose2. Remove and clean dishwasher filters3.Clear air gap debris |
| Water overflowing out of dishwasher | 1. Drain line severely blocked 2. Sink drain line clogged | 1. Flush and inspect drain line2. Plunge and snake sink drain line |
| Standing water in tub + loud grinding noise | 1. Drain pump failure 2. Bad drain impeller 3. Glass or bones lodged in pump | 1. Inspect and replace drain pump 2. Replace worn impeller3. Remove debris from pump |
| Dishwasher stops mid cycle | 1. Faulty drain valve> 2. Control board issues | 1. Inspect, clean or replace drain valve 2. Replace control board |
| Dishes left dirty with food stuck on | 1. Clogged dishwasher filters2. Low water pressure3. Spray arms not rotating | 1. Clean dishwasher filters 2. Fix home water pressure3.Repair or replace spray arms |
Key Takeaways on Dishwasher Drain Problems
Getting to the root cause of dishwasher drainage problems quickly limits water damage risks and lets you restore normal washing functionality.
In many cases, clogs from small debris cause preventable drainage failures. Regular filter cleaning and drain line maintenance eliminates many future clog-related service calls.
For appliance electrical or complex part replacements, rely on professional diagnosis and repair expertise rather than attempting dangerous DIY fixes.
Catching drainage problems quickly and keeping internal dishwasher components clear of buildup are smart ways to dodge dirty dish frustration and extend your appliance lifespan.