Quick answer
A dishwasher that won’t drain is usually caused by a clogged filter or sump, a blocked or kinked drain hose, a clogged air gap or garbage disposal inlet, or a jammed/failed drain pump. Start by cleaning the filter and sump, then check the hose routing and connections, clear the air gap (if present), and inspect the disposal inlet for the knockout plug. If the pump hums but doesn’t move water—or is silent—inspect the pump and check valve. Call a pro if you find electrical issues, leaks from the tub, or need pump/control board replacement.
What’s going on and why it matters
Dishwashers push dirty water out using a small drain pump through a hose into either an air gap and then the sink drain, or into a garbage disposal’s dishwasher inlet. Any obstruction or misrouting will stop the drain. Incorrect installation (no high loop or air gap), food debris (seeds, glass), and old hoses are common culprits. The fix is often simple and low-cost.
Common causes
- Clogged filter or sump screen (food debris, labels, glass)
- Kinked, sagging, or clogged drain hose
- Air gap clogged (if present on the sink deck)
- Garbage disposal knockout plug not removed after new disposal install
- Clogged sink tailpiece or P-trap
- Stuck check valve near the pump/sump
- Jammed or failed drain pump (broken impeller, seized motor)
- Excess suds from wrong detergent causing poor drainage
Typical specs and routing
- Drain hose: 5/8" or 3/4" ends; length per manufacturer
- High loop: secure to underside of countertop (≈ 32–34" from floor or above the dishwasher’s water level)
- Air gap: required by code in many areas; must be mounted above the sink rim
- Disposal: remove dishwasher inlet knockout plug before connecting
What you’ll need
- Screwdrivers (Phillips, flat), Torx bits (T15/T20) for toe-kick and pump covers
- Nut driver (1/4" or 5/16")
- Pliers or hose clamp pliers
- Bucket, towels, and gloves
- Flashlight/headlamp
- Wet/dry vac (helpful for clearing hoses)
- Small brush and mild dish soap
- Zip ties or a hose support clip
- Multimeter (optional, for testing pump continuity)
Step-by-step troubleshooting
1) Run a cancel/drain cycle
- Many machines have a Cancel/Drain button or require holding Start for 3–5 seconds. Listen:
- Pump running with gurgling = blockage downstream.
- Humming only = jammed impeller or seized pump.
- Silent = no power to pump or failed pump.
2) Kill power and access
- Turn off the breaker and water supply. Open the door and remove the bottom rack. Place towels to catch water. Remove the toe-kick panel with a screwdriver or nut driver.
3) Clean the filter and sump
- Remove the cylindrical filter and mesh screen in the tub bottom. Wash with warm soapy water. Inspect the sump opening with a flashlight for bones, glass, fruit pits, or labels. Carefully remove debris. This alone solves many no-drain issues. Time: 10–15 minutes. Cost: $0.
4) Check the air gap (if present)
- Twist off the air gap cap at the sink. Clear any gunk with a brush and run water through the small hose to the disposal/tailpiece. A bottle brush or a flexible pick helps. Time: 5–10 minutes.
5) Inspect the drain hose routing
- Under the sink, make sure the hose has a proper high loop or connects to an air gap. Secure it high under the countertop using a clip or zip tie. Look for kinks, sharp bends, or sags that hold water. If connected to a new disposal, confirm the knockout plug was removed (poke a screwdriver into the inlet—if solid, remove the inlet fitting and knock out the plug, then fish out the disk). Time: 10–20 minutes.
6) Clear the drain hose
- Disconnect the hose from the disposal or sink tailpiece (use pliers on the clamp). Drain into a bucket. Try blowing through the hose or use a wet/dry vac to pull from the sink end. If blocked, remove the hose at the dishwasher side (rear or side connection inside the cabinet), flush with hot water, or replace the hose if it’s brittle. New hoses cost about $10–$25. Time: 20–45 minutes.
7) Inspect the check valve
- Near the sump outlet there’s often a rubber flapper or small check valve to prevent backflow. Access from inside the sump or from below depending on model. If the flapper is stuck or deformed, clean or replace.
8) Test and inspect the drain pump
- From below, locate the drain pump (small motor with two wires and a hose). Disconnect power leads. Check for debris in the impeller housing. Spin the impeller—it should move freely. If it’s seized or the impeller is broken, replace the pump. Use a multimeter to check continuity per your model’s spec. Replacement pumps typically cost $50–$150. Time: 30–90 minutes depending on access.
9) Verify the sink drain
- If the sink backs up when you run the dishwasher drain, clear the P-trap/tailpiece. Do not use caustic drain cleaners—they can damage the dishwasher seals and pump.
Safety pointers
- Always cut power at the breaker before reaching under the unit.
- Water and electricity don’t mix—keep the area dry and wear gloves.
- Edges under the dishwasher can be sharp; use gloves and go slow.
- Avoid chemical drain cleaners with dishwashers.
Tips for best results
- Scrape heavy food into the trash, then rinse lightly—don’t overload the filter.
- Run hot water at the sink for 10–15 seconds before starting a cycle.
- Use the correct dishwasher detergent; regular dish soap creates suds that hinder draining.
- Secure a high loop even if you have an air gap—added protection against backflow.
- Keep a spare hose clamp and a couple of different-size clamps on hand for reassembly.
Common mistakes to avoid
- Forgetting to remove the disposal knockout plug after new disposal installation.
- Reinstalling a sagging drain hose without a high loop.
- Over-tightening hose clamps and cracking plastic fittings.
- Skipping the sump/filter clean—blockages often start there.
- Ignoring a humming pump; prolonged operation can overheat the motor.
When to call a pro
- You find a failed drain pump and aren’t comfortable replacing it.
- There’s evidence of leaks from the tub or door seal.
- The control board isn’t energizing the pump (needs electrical diagnosis).
- The dishwasher is under warranty—don’t risk voiding coverage.
Time and cost snapshot
- Filter/sump clean: 10–15 minutes, $0.
- Hose inspection/clear: 20–45 minutes, $0–$25 parts.
- Air gap clear: 5–10 minutes, $0.
- Drain pump replacement: 30–90 minutes, $50–$150 parts; service call typically $150–$300+ total depending on region.
With a flashlight, a couple of hand tools, and a methodical approach, most no-drain issues are solved in under an hour. If you reach the pump and it’s clean but still not running, that’s the point to price a replacement or schedule service.