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Commercial Commercial Dishwasher: Not Cleaning — Causes & Fixes

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

Quick answer: Dirty dishes almost always come down to owner-level items: wash water too cold, clogged wash/spray arms and jets, a blocked scrap screen starving the pump, no or low detergent, or dishes racked wrong (overlapping/stacked so spray can't reach them). Check the wash temperature first (chemical/low-temp machines need at least 120°F wash and 120-140°F incoming water; hot-temp machines need roughly 150°F+ wash), then clean the arms and screens, confirm detergent is feeding, and re-rack so every surface faces the spray. If wash pressure is weak after cleaning the screens and arms, the wash pump or a scaled-up system needs a technician.
Food safety: Sanitizing only works on a clean surface. Under the FDA Food Code, ware must first be washed clean, then sanitized (hot-water rinse or chemical sanitizer). Dishes coming out with visible food or film have not been effectively cleaned or sanitized and must be re-washed — serving on them is a health-code violation. 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. Wash water too cold. Check the wash-tank temperature gauge. Low-temp chemical machines need the wash tank at least 120°F with incoming water 120-140°F; high-temp machines wash hotter (about 150°F+). Cold incoming water or a marginal water heater is a common cause.
  2. Clogged wash/spray arms and jets. Inspect upper and lower wash arms and spray tips for food scraps and lime scale. Clogged jets mean uneven, weak spray and un-cleaned ware.
  3. Blocked scrap screen / pump intake starving the wash pump. A clogged scrap screen or pump-intake screen reduces the water reaching the pump, so wash pressure drops and dishes don't get scrubbed.
  4. No or low detergent. Confirm the detergent container isn't empty and the detergent (red) feed line is drawing product. Watch the detergent injection tube during a cycle. A clogged or kinked pick-up tube or clogged dispenser starves the wash.
  5. Dishes racked wrong / overloaded. Stacked, overlapping, or nested ware blocks the spray. Glasses/cups/bowls must be inverted (face down), plates racked in one layer facing the spray.
  6. Weak wash pump or scaled-up system (persistent low pressure). Wash pressure stays weak even after cleaning screens and arms.

Likely causes, checks & fixes

Likely causeHow to checkWhat to doWho
Wash water too coldCheck the wash-tank temperature gauge. Low-temp chemical machines need the wash tank at least 120°F with incoming water 120-140°F; high-temp machines wash hotter (about 150°F+). Cold incoming water or a marginal water heater is a common cause.Confirm the primary water heater is delivering hot water at temperature; on chemical machines verify soft/hot water supply. If the tank heater isn't maintaining wash temperature, call a technician — do not modify the tank heater or its wiring. · see: won't fillBasic
Clogged wash/spray arms and jetsInspect upper and lower wash arms and spray tips for food scraps and lime scale. Clogged jets mean uneven, weak spray and un-cleaned ware.Remove the wash arms, clear each jet with a toothpick, and flush the arm at the sink (the end plug can be unscrewed to rinse the tube). Reinstall the arms fully seated.DIY-safe
Blocked scrap screen / pump intake starving the wash pumpA clogged scrap screen or pump-intake screen reduces the water reaching the pump, so wash pressure drops and dishes don't get scrubbed.Remove and clean the scrap screen and inspect/clean the pump intake screen in the sump.DIY-safe
No or low detergentConfirm the detergent container isn't empty and the detergent (red) feed line is drawing product. Watch the detergent injection tube during a cycle. A clogged or kinked pick-up tube or clogged dispenser starves the wash.Refill/replace the detergent supply, straighten or clear the pick-up tube, and prime the detergent pump. Have your chemical supplier verify the feed rate if concentration stays low.DIY-safe
Dishes racked wrong / overloadedStacked, overlapping, or nested ware blocks the spray. Glasses/cups/bowls must be inverted (face down), plates racked in one layer facing the spray.Scrape and pre-rinse ware, then re-rack so no pieces overlap and every soiled surface faces the spray arm; run flatware handles-down to prevent nesting.DIY-safe
Weak wash pump or scaled-up system (persistent low pressure)Wash pressure stays weak even after cleaning screens and arms.Call a qualified technician to check the wash pump, and have the machine descaled/delimed by a qualified chemical specialist if lime buildup is found.Technician

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 cleaning?

Dirty dishes almost always come down to owner-level items: wash water too cold, clogged wash/spray arms and jets, a blocked scrap screen starving the pump, no or low detergent, or dishes racked wrong (overlapping/stacked so spray can't reach them). Check the wash temperature first (chemical/low-temp machines need at least 120°F wash and 120-140°F incoming water; hot-temp machines need roughly 150°F+ wash), then clean the arms and screens, confirm detergent is feeding, and re-rack so every surface faces the spray. If wash pressure is weak after cleaning the screens and arms, the wash pump or a scaled-up system needs a technician.

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: Weak wash pump or scaled-up system (persistent low pressure). 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.

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