Dishwasher Not Draining? Here’s How to Clear It Up
A dishwasher that won’t drain is almost always caused by a blockage — check the filter, garbage disposal connection, drain hose, and air gap first. If all four are clear, the drain pump itself has likely failed and needs professional repair.
“Water was sitting in the bottom of our dishwasher every single time. Turned out to be the drain hose was kinked behind the unit — the tech spotted it in five minutes and it’s been fine since.”
Standing water pooling at the bottom of the tub after a cycle is one of the most common dishwasher complaints in Toronto homes. The good news is that most causes are mechanical blockages rather than expensive component failures, and several of them are things a homeowner can check safely before booking a technician.
1. Clean the Drain Filter
Nearly every modern dishwasher has a removable filter assembly at the bottom of the tub, usually a cylindrical or cup-shaped piece that twists out by hand. Food particles, grease, and small bits of paper or labels collect here over time, and once the mesh is packed tight, water simply can’t pass through fast enough during the drain phase. Pull the filter, rinse it under hot water, and use an old toothbrush to work grease out of the mesh before reseating it. This single step resolves a large share of drainage complaints on its own.
2. Check the Garbage Disposal Connection
If your dishwasher’s drain hose ties into a garbage disposal or an air-gap fitting near the sink, a clog in that shared line will back water up into the dishwasher even though the dishwasher itself is working fine. A disposal that hasn’t been run in a while can build up debris in the knockout plug — the small plastic tab inside the disposal’s inlet that has to be removed during installation. If it was never knocked out, or has since clogged with food, the dishwasher has nowhere for its water to go.
3. Inspect the Drain Hose
The corrugated hose that runs from the dishwasher to the drain or disposal can kink if the unit has been pulled out and pushed back in, or during a countertop/cabinet installation. Pull the dishwasher out slightly (with power and water disconnected) and follow the hose for its full length, checking for sharp bends, pinches under the cabinet, or a visible clog near either end. A hose with a “high loop” or air-gap fitting installed incorrectly can also allow siphoning issues that mimic a drainage problem.
4. Examine the Air Gap
Many Ontario homes have a small chrome or plastic cylinder mounted on the counter or sink deck next to the faucet — this is the air gap, and its job is to prevent dirty sink water from siphoning back into the dishwasher. Debris trapped inside the air gap restricts drainage the same way a clogged filter does. Unscrew the cap, lift out the plastic insert, and clear out any buildup. If your kitchen doesn’t have a visible air gap, the drain line likely uses a high-loop configuration instead, and the hose check above becomes more relevant.
5. Test the Drain Pump
If the filter, disposal line, hose, and air gap are all clear and water is still sitting in the tub, the drain pump itself may have failed. The pump uses an impeller to push water out through the drain line, and a worn motor, a jammed impeller (often from a piece of glass or a bone fragment), or a burnt-out winding will all produce the same symptom: the dishwasher runs its cycle normally but never actually empties. Diagnosing a pump failure typically involves listening for the pump motor during the drain phase — a humming sound with no water movement usually points to a blocked or seized impeller, while total silence points to an electrical failure. Either scenario needs a technician, since the pump sits under the tub and requires disassembly to access.
Why Standing Water Shouldn’t Be Ignored
Leaving water sitting in the tub between cycles isn’t just inconvenient — it creates a breeding ground for mold and mildew, produces a sour smell that transfers onto “clean” dishes, and can eventually overflow onto the kitchen floor if a new cycle starts on top of standing water. Prolonged sitting water can also cause the rubber seals and gasket around the pump housing to degrade faster than normal.
Preventing Future Drainage Problems
Scraping large food scraps off plates before loading (rather than relying on the dishwasher to break them down), running the garbage disposal briefly before starting the dishwasher if the two share a line, and cleaning the filter every few weeks will prevent the vast majority of repeat drainage complaints. If the problem returns shortly after clearing all five of the points above, that’s usually a sign the pump is beginning to fail intermittently and worth having inspected before it stops working entirely.
Frequently Asked Questions
Is it safe to run another cycle if water is still sitting in the tub?
No — starting a new cycle on top of standing water usually just adds more water on top of the blockage and increases the risk of overflow onto the floor. Clear the blockage first, or at minimum bail out the standing water by hand before running anything else.
Why does my dishwasher drain fine sometimes but not others?
Intermittent drainage usually points to a partial clog rather than a failed pump — food debris that shifts position in the filter or hose can block flow on some cycles and clear itself on others. It’s worth cleaning the filter and checking the hose even if the problem seems to have resolved itself, since a partial clog tends to get worse over time.
Can a clogged air gap cause a bad smell even when the dishwasher isn’t running?
Yes. Standing water trapped behind a clogged air gap or in a low point of the drain hose will develop odor over a day or two, and that smell can drift up through the air gap opening on the counter even between cycles.
Does the brand of dishwasher matter for drainage problems?
Not much — filters, drain hoses, air gaps, and pump assemblies work on the same basic principles across nearly every major brand. What varies more is how accessible the filter is and whether the model uses a visible air gap or a high-loop hose configuration, which changes where you should look first.
How do I know if it’s the pump versus just a clog?
If cleaning the filter, checking the disposal connection, inspecting the hose, and clearing the air gap don’t resolve it, the pump is the next likely cause. A technician can confirm this in minutes by running a diagnostic drain cycle and listening to the pump directly, which is faster and more reliable than guessing.
*Same-day service is offered whenever possible and depends on technician availability, parts, and your location within the GTA.