1. Clogged filter or sump — the #1 cause on every brand
What it is: Bosch, Miele, KitchenAid, Whirlpool, Samsung, LG, GE all use a removable cylinder filter in the tub floor. Food debris, glass shards, and a fat-and-detergent biofilm choke the sump and the unit can't move water fast enough to drain. Symptom: standing water, foul smell, glassware comes out cloudy. We find this on roughly 1 in 3 'not draining' calls.
Fix: Twist the filter counter-clockwise, rinse under hot water with a soft brush, clear visible debris from the sump well, run an empty hot cycle with citric-acid cleaner. If that fixes it, no truck needed.
Typical all-in: DIY · $0 if it's just the filter
2. Drain hose clogged at the high loop or air gap
What it is: Code requires the drain hose to loop up under the counter or run through an air gap on the sink deck. Grease and food sediment collect at the highest point of the loop and at the air-gap inlet. Symptom: gurgling at the sink during the drain cycle, water draining back into the tub when the cycle ends.
Fix: Disconnect the drain hose at the disposal / air gap, blow it clear or replace, clean the air-gap cap. ~25-minute job.
Typical all-in: $185–$245 all-in
3. Garbage-disposal knockout plug never removed (new installs only)
What it is: Every disposal ships with a plastic plug blocking the dishwasher inlet. If your installer (or the previous owner's installer) skipped it, the dishwasher has literally nowhere to drain. Symptom: brand-new install that has never drained correctly.
Fix: Remove the disposal inlet hose, knock the plug out with a screwdriver and hammer, fish out the plug, reattach. 5-minute fix.
Typical all-in: DIY · $0
4. Failed drain pump
What it is: The drain pump is a small impeller motor under the tub. Glass, fruit pits, and twist-tie wires lodge in the impeller and seize the motor. Common at year 4–8 across all brands. Bosch, KitchenAid, and Whirlpool drain pumps are stocked on our trucks.
Fix: Pull the lower access panel, disconnect the drain pump, inspect impeller for debris and free-spin, replace OEM pump if seized or burned out. Verify drain time under 90 seconds.
Typical all-in: $245–$365 all-in
5. Failed drain check valve (back-flow flap)
What it is: A small rubber flap inside the sump prevents drained water from siphoning back into the tub. When it tears or sticks open, water from the disposal / drain line back-flows into the dishwasher. Symptom: tub fills with dirty water between cycles, even when off. Common on Whirlpool, KitchenAid, Maytag, and JennAir tall-tub platforms.
Fix: Replace the check-valve assembly (often integrated with the drain pump housing on newer models). Verify with a dye test.
Typical all-in: $225–$315 all-in
6. Bosch / Miele E24 / E25 — closed-loop drain-system fault
What it is: Bosch and Miele use a closed-loop sensored drain system. E24 means the unit detected slow drain (usually filter or hose), E25 means the drain pump can't prime. Symptom: cycle aborts mid-drain, error code on the display, water remains. Most-frequent service code on Bosch 500 / 800 series after year 3.
Fix: Clear filter and sump first (E24 often clears here). If E25 persists after a clean, replace the drain pump and verify the pressure switch / turbidity sensor in service mode.
Typical all-in: $265–$385 all-in
7. Failed main control board (rare — last suspect)
What it is: If the drain pump tests good, filter is clean, hose is clear, and the unit still won't pulse the pump, the main control board has failed. Symptom: no audible pump activity, no error code, board doesn't enter drain mode. We find this on under 5% of 'not draining' calls — almost always after a power surge.
Fix: Test pump-trigger voltage at the board harness in service mode. Replace OEM main control if no signal. Bosch / KitchenAid / Whirlpool boards are stocked.
Typical all-in: $385–$525 all-in
