Why won't my dishwasher drain?
Updated August 2026
Standing water in the bottom of the tub after a cycle points first to a clogged filter and food trap that the drain pump cannot pull through. Lift out the filter, clear the sump, and you have solved it maybe seven times out of ten, all for free. When a clean filter still leaves an inch of gray water, the trail runs to the drain hose, the garbage-disposal knockout, the air gap, and finally the drain pump itself.
Safety first: standing gray water is not an emergency, but do not leave it sitting for days: it grows bacteria and can overflow the tub if the door is bumped. Before you reach into the sump, soak up the water with a hand towel, and if you pull out broken glass, wear a glove so you do not cut yourself on shards hiding in the filter.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Clogged filter and sump | Most common | Remove the filter, scoop out the gunk in the sump below, and fish out any glass or labels blocking the pump inlet. | Free |
| Garbage-disposal knockout plug still in | Common | If a new disposal was installed and the dishwasher never drained since, the shipping knockout plug is still in place. Punch it out. | Free |
| Kinked or clogged drain hose | Common | Straighten a pinched hose behind the unit and clear grease clogs where it loops up under the sink. | $0–40 |
| Blocked air gap | Occasional | Pop the countertop air-gap cap and clean the debris packed inside it. A blocked gap backs water into the tub. | Free |
| Failed drain pump | Occasional | A pump that hums without moving water, or sits silent, has failed. A tech replaces the pump module. | $150–350 |
| Faulty drain solenoid or timer | Rare | The control never signals the drain. Diagnosis and a control or solenoid repair are a pro job. | $150–300 |
Check these first
- Scoop the standing water out with a cup and sponge so you can work, then twist out the filter and clear the sump.
- Reach into the sump and feel for glass, fruit stickers, or a chunk of food jamming the pump inlet.
- If you recently added a garbage disposal, check that the installer punched out the dishwasher knockout plug.
- Pull the machine out and look for a kinked drain hose or a high loop that has sagged flat.
- Twist off the air-gap cap on the countertop and clear any sludge inside.
- Run the cycle and listen: a healthy drain pump makes a steady whir as it empties.
Prevent it next time
Nearly every no-drain call starts with a filter nobody has touched in months. Pull and rinse it on the monthly schedule and scrape plates before loading so grease and food never reach the sump. A descaling run every couple of months keeps the drain path and pump free of the scale that narrows it. These two habits cost nothing and head off the standing-water problem entirely. If a well-maintained unit past its 12-year lifespan starts failing to drain, the pump is usually telling you the machine is near the end.
When to call a pro
Stop bailing and call a pro when the filter, hose, air gap, and knockout are all clear but the tub still holds water, which usually means a dead drain pump or a control fault. Budget $90–150 for the diagnosis and $150–350 for a drain-pump replacement. Weigh that against the age of the unit: on a dishwasher older than 10 to 12 years, a new machine often makes more sense than a pump that costs a third of its price.
Most of the causes above are maintenance problems wearing a disguise. OnOtto keeps the boring prevention on schedule so the 2 a.m. version doesn't happen.
Stop chasing symptoms, free for 30 daysFrequently asked questions
Is a little standing water in the dishwasher normal?
A small amount of clean water sitting in the filter well is normal and keeps the seals from drying out. What is not normal is an inch or more of dirty gray water across the whole tub floor after a completed cycle. That means the machine failed to pump out, and the cause is almost always a clogged filter, a blocked hose, or a stalled drain pump. Clear the filter first, and if the water returns each cycle, work down the drain path.
Can I use Drano or a chemical drain cleaner in my dishwasher?
No. Caustic drain cleaners like Drano can damage the pump seals, hoses, and the tub plastic, and they do not reach the filter and sump where dishwasher clogs actually sit. The safe fix is mechanical: remove the filter and clear the blockage by hand, or run a cup of white vinegar plus baking soda through an empty cycle to cut grease. Save chemical cleaners for sink drains, never the dishwasher, or you may turn a free fix into a repair bill.
Why won't my dishwasher drain but the garbage disposal works fine?
The two share a drain connection, so a working disposal rules out a clog past that junction and points back at the dishwasher side. The classic culprit is a garbage-disposal knockout plug: when a new disposal is installed, a shipping plug must be punched out of the dishwasher inlet, and if the installer skipped it, the dishwasher has never been able to drain. Check that first, then the dishwasher's own filter, hose, and air gap.