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Commercial Commercial Dishwasher: Not Draining — Causes & Fixes

Compiled by Resultex Media Group · Editorially reviewed · Last verified August 2026

Quick answer: Most drain problems are a clogged screen, scrap basket, or drain line, or a foreign object (a knife, fork, or spoon) jamming the drain ball/actuator — all owner-checkable. Turn the machine off, remove and clean the scrap screen and any object stuck in the drain, and check the drain line/hose for kinks or blockages. Hobart's guidance is to power the unit off, wait several seconds, then power back on and repeat to clear a drain-valve obstruction. If water still won't drain with a clear screen and drain line, the drain solenoid, drain pump, or control is at fault — that is a technician diagnosis, and the drain plumbing hard-connection is not something to modify yourself.
Food safety: A machine that won't drain washes and rinses in dirty, contaminated water and cannot properly clean or sanitize ware. Stop using it until it drains normally — soiled recirculated water can leave a food-residue film that harbors bacteria, and the sanitizing rinse cannot work on dishes that aren't clean first. Note: returning food to 41°F does not by itself make it safe. If the time/temperature history is unknown, segregate the product and follow your food-safety plan; the FDA Food Code’s time-as-a-public-health-control provisions require specific written procedures, and local health-department requirements may differ. When safety cannot be verified, discard it.

Check in this order (5-minute diagnostic)

Work top to bottom — the quickest, most-likely checks are first.

  1. Clogged drain screen / scrap basket. Remove the drain/scrap screen and look for food debris packed against it. A blocked screen or full scrap accumulator/tray stops the machine from clearing water.
  2. Foreign object jamming the drain actuator / drain ball. If the machine won't hold or won't release water, check the drain actuator/drain ball for a knife, spoon, fork, or other object holding it open or closed.
  3. Restricted or kinked drain line. Trace the drain hose/line for kinks, sharp bends, or blockage. On gravity-drain machines the drain may simply be clogged downstream.
  4. Drain-valve obstruction (electronic-control models). If draining is sluggish or incomplete, a partial obstruction may be holding the drain valve.
  5. Failed drain solenoid, drain pump, or control. Screen, scrap basket, and drain line are all clear but the machine still won't pump/drain water.

Likely causes, checks & fixes

Likely causeHow to checkWhat to doWho
Clogged drain screen / scrap basketRemove the drain/scrap screen and look for food debris packed against it. A blocked screen or full scrap accumulator/tray stops the machine from clearing water.Remove the screen and rinse all debris off at the sink or with the pre-rinse hose (do not bang it on the table). Empty the scrap tray/accumulator, then reinstall the screen in its proper position. · see: won't fillDIY-safe
Foreign object jamming the drain actuator / drain ballIf the machine won't hold or won't release water, check the drain actuator/drain ball for a knife, spoon, fork, or other object holding it open or closed.Turn the machine off, remove the object, and confirm the drain ball seats and lifts freely. · see: won't fillDIY-safe
Restricted or kinked drain lineTrace the drain hose/line for kinks, sharp bends, or blockage. On gravity-drain machines the drain may simply be clogged downstream.Straighten kinks and clear obvious blockages you can reach. If the building drain is clogged, call a plumber — do not modify the hard-piped drain connection yourself. · see: won't fillBasic
Drain-valve obstruction (electronic-control models)If draining is sluggish or incomplete, a partial obstruction may be holding the drain valve.Power the machine off, wait several seconds, then power it back on; repeat once or twice to try to clear the obstruction, per Hobart's procedure. · see: won't fillDIY-safe
Failed drain solenoid, drain pump, or controlScreen, scrap basket, and drain line are all clear but the machine still won't pump/drain water.Call a qualified service technician to test the drain solenoid/valve, drain pump, and control board. These are not owner-serviceable. · see: won't fillTechnician

Who can do it: DIY-safe owner-doable · Basic simple part swap · Technician refrigerant/gas/electrical — call a licensed pro.

How to do the safe fixes

Owner-doable procedures only. Anything on the "Technician" list above needs a licensed pro.

Clean the drain/scrap screen and scrap tray DIY-safe
  1. Turn the machine off and, if it holds water, drain it (lift the drain ball/actuator until the water is out).
  2. Lift out the drain/scrap screen and remove any foreign object (a stuck knife, fork, or spoon) from the drain area.
  3. Rinse all food debris off the screen at the sink or with the pre-rinse hose - do not bang it on the table to knock food loose.
  4. Remove and rinse the scrap tray/accumulator drawer; clean it after each meal, or hourly when very busy.
  5. Reinstall the screen in its proper position in the sump housing before refilling.

· Tools: Sink or pre-rinse hose, Disposable gloves · Source: CMA EAH/EC Owner's Manual (Cleaning the drain screen; Machine Will Not Hold Water; Empty the Scrap Tray)

Clean the wash and rinse arms and unclog spray jets DIY-safe
  1. Turn the machine off and remove the upper and lower wash/rinse arms per your manual.
  2. Hold each arm and check that water would blow from every jet; use a toothpick to open any clogged jet - do not enlarge or gouge the openings.
  3. If an arm is still restricted, unscrew the stainless end plug and flush the inside of the arm tube at the sink to clear scraps.
  4. Rinse the arms clean, reinstall the end plug hand-tight, and reseat the arms fully so they spin freely and spray reaches all ware.
  5. Run a test cycle and confirm even spray from both arms.

· Tools: Toothpick or soft pick, Sink for flushing, Disposable gloves · Source: CMA EAH/EC Owner's Manual (Cleaning the washer arms); Champion UH130 (clean spray arms)

Prime the chemical lines (detergent, rinse aid, sanitizer) DIY-safe
  1. Confirm each color-coded pick-up line is in the correct container (on CMA: red = detergent, blue = rinse aid, clear/white = sanitizer) with tube stiffeners in place so the tube can't curl and suck air.
  2. With the master switch ON, hold each prime switch until product runs through the line and discharges into the sump/injection point (no air bubbles).
  3. Run one full cycle and watch each injection tube to confirm detergent, rinse aid, and sanitizer are all feeding.
  4. On low-temp machines, test the final rinse at the surface of the ware with chlorine strips - it should read at least 50 ppm (target 50-100 ppm).
  5. If concentration is off, adjust the pump feed (CMA uses adjustable cams) or call your chemical supplier; never exceed a 6% sodium hypochlorite solution.

· Tools: Fresh chemical containers, Chlorine test strips (low-temp machines), Disposable gloves · Source: CMA EAH/EC Owner's Manual (Chemical Feeder; Activating Machine; Check Operations; 50-100 ppm)

Verify the machine is actually sanitizing DIY-safe
  1. Identify your machine type from the data plate: high-temperature (hot-water sanitizing) or low-temperature (chemical sanitizing).
  2. High-temp: run a rack and check the final rinse reaches at least 180°F at the manifold (165°F for a stationary-rack single-temperature machine); confirm the utensil surface reaches 160°F using a maximum-registering thermometer or heat-sensitive label placed on a plate through the cycle.
  3. Low-temp: run a cycle and test the final rinse at the ware surface with chlorine strips; it must read at least 50 ppm (target 50-100 ppm).
  4. Record the reading per your health department's practice.
  5. If the machine can't reach sanitizing temperature or concentration, stop using it to sanitize, manually wash-rinse-sanitize ware in a three-compartment sink, and call for service.

· Tools: Chlorine test strips (low-temp), Maximum-registering thermometer or heat-sensitive temperature label (high-temp) · Source: FDA Food Code 4-501.112 (hot water), 4-501.114 (chemical), 4-703.11 (utensil surface 160°F); CMA (50-100 ppm)

Descale / deliming - what is safe DIY vs. call a specialist Basic
  1. Confirm scale is the problem: white chalky film on tank walls, arms, jets, or booster, usually with hard water.
  2. For light routine scale, follow the deliming instructions in your machine's own manual exactly, using only the manufacturer-approved delimer, with gloves and eye protection, and rinse thoroughly.
  3. Do not mix delimer (acid) with detergent or sanitizer (chlorine) - mixing acid and bleach releases toxic gas.
  4. Heavy scale, or deliming the booster heater and internal plumbing, uses highly caustic agents - have a qualified chemical specialist do it.
  5. Prevent recurrence with water treatment to about 3.5 grains-per-gallon or softer and keep the softener charged with salt.

· Tools: Manufacturer-approved deliming product (per label), Chemical-resistant gloves and eye protection, Water-hardness test · Source: CMA EAH/EC Owner's Manual (de-liming agents are highly caustic; must be done by a qualified chemical specialist; water softening to 3.5 gpg)

Stop and call a qualified technician if:
Repair or replace? A gasket, coil cleaning, or a simple part is almost always worth fixing. Weigh replacement when the unit needs a compressor or sealed-system repair and is roughly 8–10+ years old, or when repeated service calls approach the cost of a new unit. Compare current commercial dishwashers →

Related commercial dishwasher problems

Frequently asked questions

Why is my commercial dishwasher not draining?

Most drain problems are a clogged screen, scrap basket, or drain line, or a foreign object (a knife, fork, or spoon) jamming the drain ball/actuator — all owner-checkable. Turn the machine off, remove and clean the scrap screen and any object stuck in the drain, and check the drain line/hose for kinks or blockages. Hobart's guidance is to power the unit off, wait several seconds, then power back on and repeat to clear a drain-valve obstruction. If water still won't drain with a clear screen and drain line, the drain solenoid, drain pump, or control is at fault — that is a technician diagnosis, and the drain plumbing hard-connection is not something to modify yourself.

When should I call a technician instead of fixing it myself?

Call a licensed technician for anything involving the sealed system, refrigerant, gas, or high-voltage wiring — for example: Failed drain solenoid, drain pump, or control. These are diagnostic-only for an operator.

Is it worth repairing or replacing?

Simple fixes (gaskets, coil cleaning, a single part) are worth repairing. Consider replacing when it needs a compressor or sealed-system repair and is 8–10+ years old, or when repeat service calls near the price of a new unit.

Sources