Quick answer: A dishwasher that finishes the cycle with standing water in the bottom of the tub has one of six problems, in this order of likelihood: a garbage-disposal knockout plug left in place (only on new disposal installs), a clogged filter, a kinked or clogged drain hose, a failed drain pump, a stuck check valve, or a clogged air gap. The first three are easy DIY fixes. Steps 4–6 may need a tech depending on your model.
Standing water in a dishwasher is the most common service call for that appliance. The good news is that more than half the time the fix takes 15 minutes and costs nothing. Work through these six steps in order — they go from cheapest and easiest to most involved. One important note before you start: a quarter-inch to half-inch of water in the recess around the filter is normal and intentional. The dishwasher keeps the pump seal wet between cycles. You are looking for water more than an inch deep, or water sitting in the bottom of the tub well past the drain cycle.
Step 1: Check the Garbage Disposal Knockout Plug
What to check: Did you (or a plumber) install a new garbage disposal recently? Every new disposal ships with a solid plastic knockout plug inside the dishwasher inlet port. That plug has to be hammered out before the dishwasher drain hose is connected to it. If it wasn't, the dishwasher cannot drain into the disposal — the water has nowhere to go.
What it indicates: A brand-new disposal plus a dishwasher that suddenly will not drain is almost always this. Seen a few times a month.
DIY fix: Disconnect the dishwasher drain hose from the disposal. Reach a screwdriver inside the disposal's dishwasher port and knock the plug out with a hammer. Fish the plug out of the disposal grinding chamber (this is critical — do not run the disposal with the plug inside it). Reconnect the hose with the clamp tight. Run a rinse cycle. Call a tech if: the plug was already out — move to step 2.
Step 2: Clean the Filter
What to check: Pull out the bottom rack. In the center-rear or center of the tub floor, you will see a removable cylindrical filter (most modern Bosch, KitchenAid, Whirlpool, GE, LG, and Samsung models). Twist counterclockwise and lift it out. Look for: food chunks, broken glass, paper labels from cans, pieces of plastic, hardened grease.
What it indicates: A clogged filter is the number-one drainage failure on any dishwasher more than a year old that has never been cleaned. Manufacturers recommend cleaning monthly. Most homeowners never do.
DIY fix: Rinse the filter under hot running water and scrub with an old toothbrush. Also reach into the well underneath and remove any debris around the impeller. Re-seat the filter and twist clockwise until it locks. Run a drain cycle (most models have a "drain only" hold-button combo — check your manual). Call a tech if: the filter was already clean.
Step 3: Check the Drain Hose for Kinks
What to check: Pull the dishwasher out from under the counter — turn off the breaker first, and have towels ready. Look at the corrugated white or gray drain hose running from the back of the dishwasher to the disposal or sink tailpiece. A common failure mode: the hose gets pinched against the cabinet wall when the dishwasher was shoved back in, or it sags below the high-loop point and water pools in the low spot.
What it indicates: Kinks block drainage entirely. Grease buildup inside the hose narrows the opening and causes slow drainage that gets worse over months.
DIY fix: Straighten any kink. The hose should rise up to the underside of the counter (the "high loop") before going down to the disposal — this prevents siphon-back. To check for internal clogs, disconnect both ends and blow through it. Call a tech if: the hose is clear but drainage is still slow.
Step 4: Check the Drain Pump
What to check: Start a fresh cycle and wait for the drain phase (usually 30–60 seconds in). Put your ear near the bottom-front of the dishwasher. You should hear a steady, slightly higher-pitched whine from the drain pump. Silence means a failed pump. A hum without water movement means a jammed impeller — broken glass is the usual culprit.
What it indicates: Failed pump motor, jammed impeller, or a wiring fault.
DIY fix: Power off at the breaker. Remove the filter and reach inside the sump — sometimes you can feel debris jamming the impeller and clear it with needle-nose pliers. Call a tech for actual pump replacement. The pump is under the dishwasher and requires laying the unit on its back. Cost runs $200–$340.
Step 5: Check the Check Valve
What to check: Inside the sump assembly is a small one-way flap (the check valve) that lets water flow out during drain but blocks dirty sink water from siphoning back in. When the valve is stuck open, the dishwasher can re-fill with dirty water from the disposal. When stuck closed, water cannot drain past it.
What it indicates: Mineral scale (very common with Denver's hard water) or food debris jamming the flap.
DIY fix: On some models the check valve is accessible by removing the spray arm and filter housing — inspect the flap, clean any debris, and verify it moves freely. Call a tech if: the valve is buried in the pump assembly. The part is cheap (under $25) but access can be tight.
Step 6: Check the Air Gap
What to check: Look behind your faucet on the sink deck. If you see a small chrome (or matching-finish) cylinder about an inch tall, that is your air gap. Many Denver homes have one — it is required by Colorado plumbing code in certain installs. If the air gap is clogged, drain water backs up and either dumps into the sink (you'll see water around the air gap during a cycle) or floods underneath the dishwasher.
What it indicates: A clog inside the air gap, almost always grease and food sludge.
DIY fix: Lift off the chrome cap, then the inner plastic cover. Inspect both hoses connected to the air gap underneath the sink. Run a long flexible brush or a piece of stiff wire through the air gap and both hoses to clear the clog. Call a tech if: the air gap is clean and drainage still fails — at that point the issue is upstream in the disposal or further down the sink drain.
Symptom Quick-Reference Table
| Symptom | Likely Cause | DIY Fix? | Repair Cost |
|---|---|---|---|
| Just after new disposal install | Knockout plug still in | Yes | $0 |
| Slow drainage building over months | Clogged filter | Yes | $0 |
| Sudden stop after moving the unit | Kinked drain hose | Yes | $0–$40 |
| Drain phase silent | Failed drain pump | No | $200–$340 |
| Dirty water filling tub | Stuck check valve | Maybe | $25–$220 |
| Water around air gap on counter | Clogged air gap | Yes | $0 |
When to Call (720) 447-8577
Still standing water after all six steps? Every major dishwasher brand in the Denverer metro — Bosch, Miele, KitchenAid, Whirlpool, Samsung, LG, GE, Thermador — for a $75 service visit (waived when you approve the repair). Every job comes with a 1-year parts-and-labor warranty.
Five-star rated on Google with 121 reviews. Serving Highlands Ranch, Denver, Littleton, Centennial, Aurora, Parker, Castle Rock, Lone Tree, and Greenwood Village. Denver's hard water makes filter and check-valve issues more common here than the national average — dishwasher pumps, valves, and complete sump kits are stocked on the truck for most major brands so most repairs are completed in one visit.