Dishwasher Not Draining: Find the Clog in Seven Checks

Standing water in the bottom of the tub is the symptom, and a dishwasher not draining is usually a blocked drain path rather than a failed machine. In a large share of cases the restriction sits outside the appliance: in the sump filter, in a new garbage disposal that still has its knockout plug, in a clogged air gap on the countertop, or in a drain hose that was never looped up under the counter. The most useful single correction is the disposal plug, which blocks the drain completely when it is left in and takes a pencil to test.

This post covers the order to check things in, the filter many owners do not know exists, the two installation faults behind most new install failures, the drain codes each brand uses, and the detergent and grease that narrow a drain over months. The numbers come from named primary sources: support and installation documents from Bosch, Whirlpool, GE Appliances, LG and Samsung, the InSinkErator manual, the Ohio Plumbing Code as published by the state, Minnesota’s adopted plumbing rules, and a city utility page. Claims no primary source confirms are listed at the end.

Key takeaways

GE Appliances calls 1 to 2 cups of clean water in the bottom of the tub normal on models without an ultra fine filter, so a shallow film is not automatically a fault.
Whirlpool’s test for a newly fitted garbage disposal is a pencil: if it slides about 3 inches into the disposal’s dishwasher inlet, the knockout plug is out.
Whirlpool’s installation instructions put the drain connection at least 20 inches above the floor and cap drain hose length at 10 feet.
Ohio’s published plumbing code, section 802.1.6, allows a deck-mounted air gap or a waste line that rises and is fastened under the sink rim or counter.
Bosch splits the failure by code: E22 and E24 mean a blocked filter and a drain restriction, while E25 means the drain pump itself.

What the water in the bottom is telling you

Some water in the bottom of a dishwasher is designed in. The useful questions are how much there is and whether it is clean.

GE Appliances draws the line by model. On models without an ultra fine filter, GE says “1 to 2 cups of clean water covering the bottom of the tub is normal.” On models that have one, water in the sump filter area is normal, but “the water should not cover the bottom of the tub.” A thin film of clear water in an older filterless machine is not a fault. Two inches of gray water with food in it is.

Timing matters as much as volume. If the machine drained properly for years and then slowed over a few weeks, the drain path narrowed, and the suspects are the filter, the sump, the hose and grease. If it has never drained since the dishwasher or the disposal went in, go straight to the installation checks below, which is where Whirlpool sends owners of new installs too.

The check order, from the tub outward

Work from the inside out. Every step here is reversible and needs no new part.

Kill the power at the dishwasher’s breaker before a hand goes into the sump. InSinkErator’s manual sets the same rule for the disposal: “Disconnect power before installing or servicing disposer.”
Bail the standing water out with a plastic cup and old towels. You cannot see the filter or hear the pump through four inches of water.
Pull and rinse the filter. On a Bosch, “rotate the filter knob to the left and lift up to remove,” then wash it under running water with mild soap and a soft brush.
Test the disposal inlet for the knockout plug. Whirlpool’s wording: “Insert a pencil into the inlet and feel for the knockout plug. If the pencil is able to go into the disposer inlet about 3 inches the knockout plug has been removed.”
Uncap the air gap. If a small chrome cylinder sits on the countertop behind the faucet, lift its cover, unscrew the cap, clear the chamber with a brush and pour hot water through.
Trace the drain hose from the dishwasher to the disposal or waste tee, looking for a kink, a crush, and a high loop fastened under the counter.
Open the drain pump. Last, not first. On a Bosch the pump sits under the filter behind a cover you pry off with a spoon. Bosch warns that some debris may be sharp.

If all seven come back clean and the tub still fills after every cycle, you have the answer by elimination: the drain pump or the control that drives it. That one is a service call rather than a Saturday job.

The filter many owners never knew was there

Almost every dishwasher sold in the last fifteen years has a manual filter in the floor of the tub, and almost none say on the panel when it is due.

Bosch treats it as a schedule, not a response to a fault: “For optimum results, we recommend you clean your filter every few months.” When the screen blocks badly enough Bosch throws E22: “The dishwasher filter is blocked. The filter is the area where food particles get caught and it needs to be cleaned regularly.”

GE splits the same job in two. Its instruction is to “remove and check the Fine and Ultra Fine filters in the bottom of the dishwasher,” then make sure nothing is “covering or blocking the sump area.” The offenders GE names are noodles, lettuce and bones. Whirlpool’s F9E1 code, labeled “Long Drain,” puts the filter first in its own list of four checks, and a long drain code is the mild version of this failure: the pump turns, but the water leaves too slowly. A filter that looks clean can still be greased over, so hold it to a light and check you can see through the fine mesh.

The disposal knockout plug, the most common new install fault

This is the fault that makes a brand new dishwasher look broken on day one, and it belongs to the disposal.

A food waste disposer ships with a molded plug sealing the dishwasher inlet on its side, because plenty of kitchens have no dishwasher to connect. If the installer never knocks that plug out, the dishwasher pumps into a closed pipe. InSinkErator’s manual states the consequence as a warning: “Risk of property damage. If connecting a dishwasher, the dishwasher inlet plug MUST be removed or the dishwasher may overflow.”

Whirlpool’s verification test needs nothing you do not already own. “Insert a pencil into the inlet and feel for the knockout plug. If the pencil is able to go into the disposer inlet about 3 inches the knockout plug has been removed.” Three inches of clear travel means the plug is out. An inch and a hard stop means it is still there, and no amount of filter cleaning will help. LG says the same under its OE code, and Samsung calls it the disposal cap.

One habit is worth building. GE tells owners to “always turn on your garbage disposer prior to running the dishwasher to clean out any food or debris within the drain system.” A disposal packed with yesterday’s scraps is a restriction whether or not the plug is out. If the unit hums, trips its reset or does nothing, a garbage disposal that will not run is a separate repair and comes first.

The air gap, and what the plumbing code actually requires

The small chrome cylinder on the countertop behind some faucets is an air gap. It exists to stop sink waste water siphoning back into the dishwasher.

The code language is worth reading once, because it tells you which of two arrangements your kitchen should have. The Ohio Plumbing Code as published by the state, section 802.1.6, says the waste line of a domestic dishwashing machine discharging into a kitchen sink tailpiece or food waste disposer “shall connect to a deck-mounted air gap or the waste line shall rise and be securely fastened to the underside of the sink rim or counter.” North Carolina’s Office of the State Fire Marshal reached the same conclusion in a published interpretation.

Some states are stricter. Minnesota adopts the Uniform Plumbing Code, and section 807.3 as published by the Minnesota Revisor of Statutes reads: “No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the use of an approved dishwasher air gap fitting on the discharge side.” The same rule adds that listed air gaps go in with the flood level marking at or above the flood level of the sink or drainboard, whichever is higher. An arrangement that is legal in one state is not a substitute in another, so check the code your jurisdiction adopted.

An air gap also clogs, because the whole discharge passes through its small chamber. GE’s instruction is direct: “remove the cap on the air gap and clean out any build-up of debris.” A clogged air gap has a signature: water spitting onto the countertop during the drain cycle.

The drain hose high loop and the numbers behind it

If your kitchen has no air gap, the drain hose does that work alone, and the way it is routed is not a matter of taste.

Whirlpool’s installation instructions carry the measurements. The drain hose connection must sit “at least 20 inches above the floor,” and Whirlpool recommends the hose “be looped up and securely fastened to the underside of the counter.” Where the house plumbing connection is lower than 18 inches, the same document calls for an air gap. Total length “must not exceed 10 ft for proper drain operation,” and you may add up to 42 inches to the factory hose.

Requirement	The figure	Source
Minimum height of the drain connection above the floor	20 inches	Whirlpool W10702387
Connection height below which an air gap is called for	18 inches	Whirlpool W10702387
Maximum total drain hose length	10 feet	Whirlpool W10702387
Maximum extension added to the factory hose	42 inches	Whirlpool W10702387

GE is blunt that this is pass or fail. The drain hose “must contain a high drain loop for the dishwasher to be able to drain correctly,” and that loop “must be attached to the underside of the counter.” Samsung names a hose with no air gap and no high loop as a leading cause.

Fixing a missing high loop costs a zip tie. Lift the hose so its highest point is tight under the countertop, fasten it there, and leave no sag between the loop and the disposal inlet. A high loop cannot fix a blocked branch drain, though. If the sink itself drains slowly with the dishwasher off at the panel, the restriction is downstream of everything above, and the job becomes how to snake a drain rather than an appliance repair.

Error codes, and what each brand means by them

A code narrows the search, because most brands separate a drain restriction from a pump that will not run.

Code	What the manufacturer says it means	Check first
Bosch E22	The dishwasher filter is blocked	Pull and wash the filter
Bosch E24	Not draining properly because the drain filter is blocked	Filter, hose kinks, pump cover, disposal plug
Bosch E25	The drain pump is blocked, or its cover is loose or missing	The pump cover under the filter
Whirlpool F9E1	Long drain	Filter, drain hose, disposal plug, air gap
LG OE	A drain issue, most often food clogs or an installation issue	Filter, hose kinks, air gap, disposal plug
Samsung 5C, SC, 5E, SE	The dishwasher cannot drain	Filter area, high loop, disposal cap

Bosch’s E24 page tells owners to confirm that the pump cover under the filter is not loose and that the disposal drain plug was removed: a factory page pointing at the plumbing, not the appliance. A machine with no display still gives you a path. LG offers a drain only routine through its cancel and drain option, and forcing a drain with the filter out tells you in a minute whether the pump turns at all.

Detergent, grease and what never goes in

A drain path that narrows over months is usually chemistry rather than mechanics, and two substances do most of the damage.

Grease is the first. The City of Columbus states the mechanism plainly: fats, oils and grease “will clog sewer pipes, which can then cause costly sewer overflows and basement backups.” The same film builds on a dishwasher filter, in the sump and inside an air gap chamber, where it catches every scrap that arrives after it. Scraping plates into the bin instead of rinsing them into the disposal is the cheapest drain maintenance there is.

Detergent is the second. GE states that “using the wrong type or too much detergent can cause over-sudsing that prevent the dishwasher from draining properly.” Whirlpool adds that household detergents made for hand washing “can generate excessive suds when used in dishwashers.” Whirlpool’s own remedy for a tub full of suds is to stop the machine, take the dishes out, add a quarter cup of cooking oil, and run a quick cycle with no detergent and no dishes.

What does not belong in the machine at any point is a drain chemical. Whirlpool’s guidance is explicit: “Do not use drain-opening chemicals inside the dishwasher; they can damage components and create safety hazards.” InSinkErator lists caustic drain cleaners among the products that must never go into a disposal.

When to stop and call a professional

Parts of this job are not do it yourself work, and the boundary is not blurry.

Kill the power at the breaker before a hand goes into the sump, every time. The drain pump is a motor under the tub floor, and a dishwasher interrupted mid cycle can restart the moment power comes back. InSinkErator applies the same rule to the disposal: “Turn off electrical power at fuse box before beginning installation.” The door switch is not an isolator.

Stop and call for service if the tub fills again after every cycle when the filter is clean, the disposal plug is out, the air gap is clear and the hose is unkinked and looped. By elimination that is the drain pump or its control board, both behind the lower access panel and both needing water and power isolated first. HomeAdvisor’s dishwasher repair cost guide, updated on June 17, 2026, publishes a normal range of $160 to $300 for dishwasher repair, $50 to $400 for a not draining fault, and $400 to $600 for a motor and pump assembly. Set that against the price of a new machine before authorizing the work, using the same arithmetic that decides when to replace your water heater.

Call a plumber rather than an appliance technician if waste water backs up into the sink or onto the floor, if the air gap spits water that smells of sewage, or if more than one fixture drains slowly at once. That pattern points at a branch line or the main. The City of Columbus notes that plumber fees vary from $200 to $400 for the first hour of response, with extra charges for additional time and after hours calls.

Hand over anything behind a wall, any electrical connection you cannot isolate at the panel, and any standing water that has reached flooring or a cabinet base. Water under a cabinet does structural damage quietly.

Frequently asked questions

How much water in the bottom of a dishwasher is normal?

GE Appliances says 1 to 2 cups of clean water covering the bottom of the tub is normal on models without an ultra fine filter. On models that have one, water in the sump filter area is normal but should not cover the tub floor. Dirty water, or a level that has risen, is a restriction.

Can drain cleaner be poured into a dishwasher that will not drain?

No. Whirlpool’s guidance is to avoid drain opening chemicals inside the dishwasher because they can damage components and create safety hazards. In a machine that is already not draining, the chemical sits against the plastic sump and the seals instead of flushing away.

How can you tell whether the garbage disposal knockout plug was removed?

Use Whirlpool’s pencil test. Push a pencil into the disposal’s dishwasher inlet and feel for the plug. Whirlpool’s wording is that if the pencil can go in about 3 inches, the knockout plug has been removed. A hard stop after an inch means the dishwasher has nowhere to pump.

Does a dishwasher need an air gap, or is a high loop enough?

It depends on the code your state adopted. Ohio’s published plumbing code, section 802.1.6, accepts either a deck-mounted air gap or a waste line that rises and is fastened under the sink rim or counter. Minnesota’s rule requires an approved air gap fitting on the discharge side. Check locally first.

Why does a dishwasher only fail to drain sometimes?

Intermittent failure usually means a partial restriction rather than a blockage. Whirlpool notes that water slightly above the filter screen often indicates a partial restriction in the filter, sump or hose, so a heavy load of greasy plates fails while a light load drains. Suds do the same.

The order is what saves the afternoon: bail the water, pull the filter, test the disposal inlet with a pencil, uncap the air gap, then follow the hose to the cabinet wall. Those five cost nothing, and three of them are installation faults that were never the dishwasher’s doing. If all five check out and the tub still holds water, you have a pump, and you know it before anyone bills you to find out.

Dishwasher Not Draining Is Usually a Clog You Can Clear