Dishwasher Not Draining: Causes and How to Fix It
Updated · from manufacturer service documentation
A dishwasher that leaves standing water in the tub almost always has a blocked filter, a kinked or improperly installed drain hose, or a clogged air gap — service documentation across brands points to the same short list of causes, most fixable without replacing the drain pump. Techs across brands report that drain pumps get replaced far more often than they should; check the hose and filter first.
What Causes a Dishwasher Not to Drain
| Cause | Likelihood | DIY difficulty | Related part |
|---|---|---|---|
| Sump/filter assembly not cleaned or blocked | Most common | Easy — remove and rinse | Filter assembly |
| Drain hose kinked, blocked, or missing its high loop | Common | Easy — check hose routing | Drain hose |
| Air gap clogged | Common | Easy — clean air gap | Air gap |
| Garbage disposal knockout plug not removed (new installs) | Common on new installs | Easy — remove plug | — |
| Inner hole of the drain case blocked | Less common | Moderate — access sump | Drain case |
| Drain motor/pump impeller stuck | Less common | Moderate — inspect pump | Drain pump assembly |
| Wiring connection to the drain motor loose or damaged | Less common | Moderate — check connector | Wiring harness |
| Washing/drain motor locked or defective | Rare | Pro repair | Drain motor |
| Main controller damaged | Rare | Pro repair | Control board |
How to Fix a Dishwasher That Won't Drain, Step by Step
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Clean the sump filter
Per service documentation across brands, this is the single most overlooked cause — many owners don't know the filter exists. Remove it, rinse out food debris, and reinstall.
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Check the drain hose routing before suspecting the pump
Confirm the hose has a proper high loop (or air gap) and isn't kinked or pinched anywhere between the dishwasher and the sink drain/disposal connection — missing high loops and pinched hoses are a documented top cause of poor draining, and a lot of good drain pumps get replaced unnecessarily because this was never checked first.
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On a newly installed dishwasher, check for the garbage disposal knockout plug
If the disposal's inlet knockout plug was never removed, the dishwasher can fill the disposal but never actually drain anywhere.
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Clean the air gap
If your installation uses an air gap fitting (usually a small cylinder on the sink deck), unclip the cover and clear any buildup — a clogged air gap stops drainage even with a perfectly good pump.
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Check the drain case and impeller for blockages
With power removed, inspect the inner drain case opening and the drain motor's impeller for anything stuck or jammed.
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Check the wiring to the drain motor
A loose or damaged connector will stop the drain pump from running even though nothing is mechanically blocked.
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If all of the above check out, the drain motor or controller may be at fault
This is the point where a technician's diagnosis is worth it — replacing a drain pump or control board without ruling out steps 1–6 first is the most common misdiagnosis reported in service documentation.
Where This Comes From
Cross-referenced from Bosch general service/repair documentation, GE's GDT-series service guide, and LG's LDF5545ST/LDT7808ST dishwasher service manual — the same core causes (filter, hose routing, air gap, blocked drain case, motor/impeller, wiring, controller) appear independently across all three brands' documentation, which is why this is written as a brand-agnostic symptom page. For brand-specific error codes tied to draining, see that brand's dishwasher error code pages.
Frequently Asked Questions
Do I need to replace the drain pump if my dishwasher won't drain?
Not necessarily, and often not at all — service documentation specifically warns that drain pumps get replaced far more often than needed when the real problem is hose installation (missing high loop, kinked hose) or a dirty filter.
Why does my new dishwasher not drain at all?
Check for the garbage disposal knockout plug first — on new installations connected to a disposal, this plug is sometimes left in place, which blocks the drain path entirely even though everything else is installed correctly.
Is a smelly dishwasher related to drainage?
Yes — a dirty filter, a missing high loop on the drain hose, or drain gases coming back through the system are documented causes of both smell and poor draining at the same time.
When is a dishwasher not draining a job for a technician?
Once you've cleaned the filter, checked the hose routing and air gap, and confirmed the drain case/impeller aren't blocked, a persistent no-drain condition points to the drain motor, wiring, or control board — that level of diagnosis is worth a professional visit.
Based on Bosch general dishwasher service/repair documentation, the GE GDT-series service guide, and the LG LDF5545ST/LDT7808ST dishwasher service manual. Last updated: .