Dishwasher Not Draining? 7 Causes & Simple Fixes

Before diving into pumps, hoses, or control issues, it’s important to start with the simplest and most frequent reason a dishwasher isn’t draining: a clogged filter or drain trap. This is the first place water passes through after a wash cycle, and it’s where food debris, grease, and soap residue collect over time. When this area becomes blocked, the dishwasher does not drain properly, leaving standing water at the bottom of the tub. The good news? It’s often the easiest part to check and clean, and for many homeowners, this single step is enough to restore normal draining without any tools or major repairs.

1. Clogged Dishwasher Filter (The Most Common Cause)

If your dishwasher isn’t draining, a clogged filter is the number one thing to check. The filter sits at the bottom of the dishwasher and traps food particles, pasta, rice, seeds, grease, and soap residue. Over time, this buildup blocks water flow and prevents the dishwasher from draining properly. In many homes, a blocked filter is the entire reason the dishwasher does not drain after a wash cycle.

Why It Happens

Dishwashers circulate the same water through the filter multiple times during a cycle. When the filter becomes full, it restricts the water pathway, causing:

• Standing water in the bottom of the dishwasher

• Dirty or greasy dishes

• Slow or incomplete draining

• Odors or unpleasant smells
  

Cold weather can make grease buildup even worse, turning soft debris into hardened blockage inside the filter housing.

How to Fix It

Cleaning the filter is one of the easiest steps when learning how to fix a blocked dishwasher:

1. Remove the bottom rack of the dishwasher

2. Locate the round or cylinder-shaped filter at the bottom

3. Twist and lift it out (usually counterclockwise)

4. Rinse under hot water to remove grease and debris

5. Use a soft brush to remove stubborn buildup

6. Wipe the filter housing before reinstalling

7. Lock the filter back into position
   

Most manufacturers recommend cleaning the filter at least once a month, but many people forget making this the single most common drainage issue.

2. Blocked Drain Trap

If the filter is clean but your dishwasher isn’t draining, the next place to look is the dishwasher drain trap. This is the area where food debris, grease, and small particles settle before entering the drain hose. When the drain trap becomes blocked, water cannot pass through properly, leading to standing water at the bottom of the dishwasher after every cycle.

Why It Happens

Cold cycles, heavy meals, and certain food types (like rice, pasta, seeds, egg shells, coffee grounds) tend to collect inside the drain trap. Over time, this debris builds up and creates a blockage. In winter months, grease solidifies faster, making clogs even more common.

A trapped blockage can cause:

• Water pooling above the trap

• Slow draining

• Gurgling noises during the drain cycle

• Musty or sour smells

For many homeowners, this hidden area is the real reason the dishwasher does not drain even if the filter is clean.

How to Fix It

Cleaning the drain trap is a simple step in learning how to fix a blocked dishwasher:

1. Remove the bottom rack of the dishwasher

2. Locate the drain trap area beneath the filter

3. Unscrew or lift the trap cover (varies by model)

4. Clear away any visible debris, food chunks, grease, seeds, etc.

5. Rinse the trap with hot water

6. Use a soft brush or cloth to scrub away hardened buildup

7. Reinstall the cover securely

For many households, this step alone solves the drainage issue without needing any tools or parts.

3. Blocked or Kinked Drain Hose

If your dishwasher isn’t draining even after cleaning the filter and drain trap, the next area to inspect is the drain hose the long, flexible tube that carries wastewater from the dishwasher to the sink drain or garbage disposal. When this hose becomes blocked, kinked, or partially collapsed, water simply cannot exit the machine, leading to standing water after every wash cycle.

Why It Happens

The drain hose can easily become restricted for several reasons:

• Food debris and grease buildup traveling through the hose

• Kinks formed when the dishwasher is pushed back too tightly against the wall

• Improper installation causing the hose to sag or bend

• Mineral buildup inside the hose, especially in areas with hard water

• Ice or cold-related stiffening in winter that limits water flow

A blocked drain hose is one of the most common hidden causes when a dishwasher does not drain, especially in older or heavily used machines.

How to Fix It

Here’s how to check and clear the hose an important step in how to fix a blocked dishwasher:

1. Turn off power to the dishwasher for safety

2. Gently pull the dishwasher forward to access the hose behind it

3. Inspect the hose for obvious kinks or crimped areas

4. Disconnect the hose from the sink drain or garbage disposal

5. Place a bucket underneath and check for a strong water flow

6. If flow is weak, flush the hose with hot water to break down grease

7. Use a long, flexible brush or drain snake to clear deeper blockages

8. Reinstall the hose and ensure it has a smooth, elevated loop (high-loop method)

A properly mounted and unobstructed drain hose is essential for reliable draining. If the hose is old, brittle, or permanently kinked, replacing it is affordable and often faster than trying to revive it.

4. Garbage Disposal Knockout Plug or Sink Drain Blockage

If your dishwasher isn’t draining and you recently installed a garbage disposal or the sink has been draining slowly the issue may not be inside the dishwasher at all. Instead, the problem could be coming from the sink drain or the knockout plug inside the garbage disposal. This hidden plug must be removed for the dishwasher to drain properly. When it’s left in place, water has nowhere to go and backs up inside the dishwasher.

Why It Happens

Here’s why this problem is incredibly common:

• New garbage disposal installed but knockout plug not removed
  - Standing water appears in the dishwasher immediately

• Sink drain clogged with grease or food debris
  - Dishwasher shares the same drain line, so it backs up

• Disposal isn’t running regularly
  - Food buildup becomes hardened and blocks the drain

• Holiday/winter usage increases
  - More cooking = more sink debris = more drainage issues

When the disposal or sink drain is blocked, the dishwasher does not drain because water can’t exit through the shared line.

How to Fix It

Here’s how to quickly diagnose and fix this issue:

1. Run the garbage disposal for 20–30 seconds
   This clears any soft debris in the drain line.

2. Check if the dishwasher drain hose is connected to the disposal
   If yes → proceed with knockout plug check.

3. Inspect the knockout plug inside the disposal

   • Disconnect the drain hose

   • Use a screwdriver to feel inside the inlet
     If you feel a solid plastic wall → plug was never removed

4. Knock the plug out (if still present)

   • Use a screwdriver and hammer

   • Remove the plastic piece from inside the disposal

   • Reconnect the hose securely

5. If sink itself drains slowly

   • Use boiling water, baking soda + vinegar

   • Or clear P-trap under the sink

   • Professional drain cleaning may be needed for heavy grease

Once the disposal and sink drain are clear, your dishwasher should drain normally again.

5. Faulty Drain Pump

If your dishwasher isn’t draining even after clearing the filter, drain trap, hose, and disposal, the next most likely issue is a faulty drain pump. The drain pump is the component responsible for pushing dirty water out of the dishwasher and into the drain line. When it becomes blocked, jammed, or stops working altogether, the dishwasher does not drain leaving water pooled at the bottom after every wash cycle.

Why It Happens

Drain pumps fail for a few common reasons:

• Foreign objects blocking the impeller
  (glass shards, seeds, food pieces, labels, broken plastic)

• Grease buildup hardening around the impeller

• Worn-out pump motor
  (common in older dishwashers)

• Electrical failure in the pump circuit

• Water intrusion into the motor housing

A pump issue often appears gradually at first slow draining before eventually turning into a complete drainage failure.

Common Signs of a Bad Drain Pump

Here’s what you might notice:

• A humming noise when the dishwasher tries to drain

• A grinding sound (impeller jammed)

• Water remaining at the bottom every cycle

• Dishwasher stops mid-cycle or restarts

• Pump runs but no water movement occurs

• Error codes related to drainage (varies by brand)

If you hear humming but no water movement, the pump is trying to work but is blocked. If you hear silence, the motor may have burned out.

How to Fix It

A drain pump is more advanced than filter cleaning, but here’s the general approach:

1. Disconnect power to the dishwasher

2. Remove the bottom access panel

3. Locate the drain pump near the bottom front area

4. Inspect the pump housing for debris

5. Carefully remove impeller blockages

6. Test the pump manually for smooth rotation

7. Reassemble and test a short cycle

If the pump motor shows no response at all or continues making a loud humming sound, it likely needs replacement.

Important Note

Replacing a drain pump generally requires:

• Basic electrical safety skills

• Ability to remove the dishwasher

• Correct OEM replacement part

• Proper sealing to avoid leaks

Because of this, many homeowners choose to call a technician once the issue reaches the pump stage.

6. Air Gap Blockage (If Your Kitchen Has One)

If your dishwasher isn’t draining and you notice water bubbling or leaking near the sink faucet area, the problem might be tied to the air gap a small metal or plastic cylinder installed beside some kitchen faucets. Not every home has one, but where it exists, it plays a critical role in preventing dirty sink water from flowing back into the dishwasher. When the air gap becomes clogged, water cannot pass through properly, causing the dishwasher to stop draining.

Why It Happens

The air gap is essentially a pressure release system, and over time, it can collect:

• Food debris

• Grease

• Soap foam

• Mineral deposits

• Small particles flushed from the dishwasher

During heavy dishwashing periods (holidays, winter cooking), buildup happens much faster, making “air gap blockage” one of the easiest-to-overlook reasons a dishwasher does not drain.

Common Signs of an Air Gap Issue

• Water leaking from the top of the air gap cap

• Gurgling or bubbling sounds in the sink during drain cycle

• Standing water inside the dishwasher

• Slow draining or intermittent draining

• Soggy food particles around the air gap opening

If you ever see water spraying or dripping from the air gap when the dishwasher runs, that’s a guaranteed indicator of blockage.

How to Fix It

Cleaning an air gap is simple and one of the quickest solutions when learning how to fix a blocked dishwasher:

1. Pull off the air gap cap (usually just lifts off)

2. Remove the inner plastic piece

3. Clear out visible debris or food particles

4. Rinse both pieces under hot water

5. Use a small brush or toothpick to break up stubborn residue

6. Run the dishwasher’s drain cycle to test flow

7. Reinstall the air gap components

If the air gap continues to overflow after cleaning, the blockage may be farther down the drain line or in the disposal connection meaning the issue isn’t just the air gap but the entire drain path.

7. Malfunctioning Door Switch or Control Board

If your dishwasher isn’t draining and all the mechanical components appear clean and functional, the issue may be related to the electrical system, specifically the door switch or control board. Modern dishwashers rely heavily on sensors and electronic signals. When those signals fail, the dishwasher may run part of a cycle but refuse to drain, because it “thinks” the door is open or the cycle didn't complete properly.

Why It Happens

Electrical and control-related failures usually occur due to:

• Worn-out door latch or loose door alignment

• A defective door switch that fails to send the “closed” signal

• Moisture or steam damage affecting internal electronics

• A failing relay on the control board

• Power surges that damage motherboard circuits

• Wiring harness issues or corroded connectors

These problems are less common than clogs or drain hose issues but when they happen, they cause complete drainage failure.

Common Signs of a Door Switch or Control Issue

• Dishwasher stops mid-cycle unexpectedly

• Nothing happens when you press “Start” unless the door is pushed firmly

• Clicking sound when closing the door is missing or weak

• Flashing lights or blinking error indicators

• Dishwasher fills and washes, but does not drain

• The control panel becomes unresponsive or resets itself

These symptoms typically point to the control system failing to complete the drainage command.

How to Fix It

Door switch and control board problems often require more technical steps:

1. Ensure the door closes tightly and evenly

2. Check if pushing the door inward makes the machine respond

3. Inspect latch for cracks or looseness

4. Reset the dishwasher by flipping the breaker OFF for 5 minutes

5. Test the drain cycle after power reset

6. If the issue returns → the switch or control board needs diagnosis

Replacing a door switch is relatively affordable, but control board repairs depend on the brand and model.

Because these are electrical components, they’re usually not recommended for DIY replacement unless you’re experienced with appliance wiring.

However, if you've worked through these troubleshooting steps and your dishwasher still refuses to drain properly, or if you're uncomfortable performing any of these checks yourself, professional help ensures the problem gets fixed correctly the first time. At Promix Appliance Repair, our experienced technicians have the tools and expertise to diagnose and repair any dishwasher drainage issue quickly and efficiently. Contact us today for same-day appliance repair in MetroWest, MA.