Commercial Commercial Dishwasher: Won't Start — Causes & Fixes
Compiled by Resultex Media Group · Editorially reviewed · Last verified August 2026
Check in this order (5-minute diagnostic)
Work top to bottom — the quickest, most-likely checks are first.
- Circuit breaker tripped / not powered. Check the breaker feeding the dishwasher and that any cord/hard-wire connection is intact.
- Master / power switch off. Confirm the machine's master/power switch on the control box is ON.
- Door not fully closed / door error. Door-type machines only run with the door fully closed; a partly open or misaligned door stops the cycle and may show a door code.
- Faulty door/safety switch, start switch, relay, or timer/control. Power is on and the door is closed but nothing happens (or it only runs while the start switch is held) — points to the door safety switch, start/stop micro-switch, start relay, or timer/control board.
Likely causes, checks & fixes
| Likely cause | How to check | What to do | Who |
|---|---|---|---|
| Circuit breaker tripped / not powered | Check the breaker feeding the dishwasher and that any cord/hard-wire connection is intact. | Reset the breaker and restore power. If it trips again, stop and have an electrician diagnose it — do not keep resetting a tripping breaker. | DIY-safe |
| Master / power switch off | Confirm the machine's master/power switch on the control box is ON. | Turn the master/power switch ON. If it's faulty, it must be replaced by a technician. | DIY-safe |
| Door not fully closed / door error | Door-type machines only run with the door fully closed; a partly open or misaligned door stops the cycle and may show a door code. | Close the door completely; if a door error shows, open and close the door to clear it. | DIY-safe |
| Faulty door/safety switch, start switch, relay, or timer/control | Power is on and the door is closed but nothing happens (or it only runs while the start switch is held) — points to the door safety switch, start/stop micro-switch, start relay, or timer/control board. | Call a qualified technician to test and replace the switch, relay, or control. These are inside the electrical enclosure and are not owner-serviceable. | 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
- Turn the machine off and, if it holds water, drain it (lift the drain ball/actuator until the water is out).
- Lift out the drain/scrap screen and remove any foreign object (a stuck knife, fork, or spoon) from the drain area.
- 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.
- Remove and rinse the scrap tray/accumulator drawer; clean it after each meal, or hourly when very busy.
- 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
- Turn the machine off and remove the upper and lower wash/rinse arms per your manual.
- 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.
- 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.
- Rinse the arms clean, reinstall the end plug hand-tight, and reseat the arms fully so they spin freely and spray reaches all ware.
- 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
- 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.
- 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).
- Run one full cycle and watch each injection tube to confirm detergent, rinse aid, and sanitizer are all feeding.
- 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).
- 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
- Identify your machine type from the data plate: high-temperature (hot-water sanitizing) or low-temperature (chemical sanitizing).
- 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.
- 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).
- Record the reading per your health department's practice.
- 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
- Confirm scale is the problem: white chalky film on tank walls, arms, jets, or booster, usually with hard water.
- 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.
- Do not mix delimer (acid) with detergent or sanitizer (chlorine) - mixing acid and bleach releases toxic gas.
- Heavy scale, or deliming the booster heater and internal plumbing, uses highly caustic agents - have a qualified chemical specialist do it.
- 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)
- Faulty door/safety switch, start switch, relay, or timer/control
- A breaker that trips again after you reset it once — stop, disconnect the unit, and call an electrician or refrigeration technician.
- You smell gas, see refrigerant/oil leaking, or the repair needs the sealed system, gas train, or high-voltage wiring.
Related commercial dishwasher problems
Frequently asked questions
Why is my commercial dishwasher won't start?
A dead machine is usually power or an interlock, and both are owner-checkable: confirm the wall circuit breaker is on and the machine's power/master switch is ON, and make sure the door is fully closed (door-type machines won't run with the door open, and a machine may show a door error). Cycling the door open and closed clears many no-start situations. If power is confirmed, the door is closed, and it still won't start, the fault is in the door/safety switch, start micro-switch, control relay, or timer/control board — a technician diagnosis, since it's inside the electrical enclosure.
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: Faulty door/safety switch, start switch, relay, or timer/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.
- CMA Dishmachines EAH/EC/3-Door Owner's Manual (Installation & Operation, Rev 1.03) - troubleshooting, cleaning, chemical feed, 50-100 ppm chlorine, wash/rinse temperatures — source
- CMA Dishmachines - How to Troubleshoot & Repair Commercial Dishwasher — source
- Hobart Dishwasher Troubleshooting Guide (Parts Town resource center) — source
- Jackson 24A-AF Instruction Manual - Troubleshooting Guide (ManualsLib) — source
- Jackson Dishwasher Troubleshooting (Parts Town resource center) - spotting/hard water, leveling — source
- Champion UH130 Installation/Operation Manual with Service Replacement Parts - Maintenance & Troubleshooting (ManualsLib) — source
- Champion Dishwasher Troubleshooting (Parts Town resource center) — source
- FDA Food Code - mechanical warewashing sanitization: hot water rinse temperatures (4-501.112), utensil surface 160°F (4-703.11), chemical/chlorine sanitizer concentration 50-100 ppm (4-501.114), test devices (4-302.14 / 4-501.116) — source
- NSF/ANSI 3 - Commercial Warewashing Equipment (sanitization performance standard for dish machines) — source
- OSHA - restaurant/foodservice hazards (wet-floor slips, chemical handling) — source