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Fix a commercial dishwasher that will not sanitize

We'll confirm the symptom, determine high-temp vs low-temp, then check water temp, booster heater, or chemical sanitizer—or tell you when to call a pro.

Troubleshooting · Home appliances
15–45 min
What you'll need
  • Thermometer (for water temp check)
  • Multimeter (for heater and thermostat continuity tests)
  • Screwdriver set (Phillips and flathead)
  • Replacement booster heater or thermostat (if tests show a fault)
Step 1 of 10

Quick triage — pick your path

Quick triage — pick your path

Choose the option that matches what you see. You can jump straight to that section.

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Steps

Goal: Confirm the symptom, determine machine type, then isolate the cause—water temp, booster heater, or chemical sanitizer.

Check water temperature

Goal: Rule out low incoming water temp before opening the machine.

  • Run hot water at the nearest prep sink for one minute. Measure with a thermometer at the faucet.
  • High-temp machines need at least 120°F (49°C) incoming. Low-temp machines need 100°F (38°C) or per manufacturer.
  • If the water is too cold, raise the water heater or check the hot water line for restrictions.
  • Good: Temp meets minimum. Proceed to High-temp path or Low-temp path based on your machine type.
  • Bad: Water too cold—fix the water supply first. Retest after raising the water heater.

High-temp path

Goal: Test and replace the booster heater or thermostat on a high-temp commercial dishwasher.

  • Determine that your machine is high-temp (uses a booster heater for 180°F rinse). Unplug the machine and shut off water.
  • Access the booster heater per your model—often under the tank or behind a panel. Check your owner’s manual or search “[brand] [model] commercial dishwasher service manual” for disassembly steps.
  • Test the heater for continuity with a multimeter. No continuity means replace the heater with a matching part (match the part number).
  • If the heater is good, locate the thermostat near the heater. Test for continuity at room temperature. Replace if faulty.
  • Remove and inspect the rinse arm for clogged holes. Clear scale or debris with a toothpick or soft brush. Reinstall.
  • Good: You found and replaced the faulty part. Reassemble and test—the machine should sanitize.
  • Bad: All parts test good but it still fails—call a technician.

Low-temp path

Goal: Check the sanitizer tank and injector on a low-temp commercial dishwasher.

  • Confirm your machine is low-temp (uses chemical sanitizer). Check the sanitizer injector tank—refill if empty or low with the correct chemical per the manufacturer.
  • Locate the injector per your model—often near the pump or chemical line. Remove and inspect for clogs or mineral buildup. Clean or replace if blocked.
  • Confirm the injector tubing is not kinked. Check that the pump runs during the rinse phase.
  • Good: Sanitizer flows and the machine sanitizes.
  • Bad: Tank is full and injector is clear but it still fails—call a technician.

When to get help

Call a commercial kitchen technician if:

  • The booster heater or thermostat tests faulty and you are not comfortable replacing them.
  • You smell gas near a gas-heated booster—shut off the machine and call from outside.
  • You have checked water temp and sanitizer and it still fails.
  • The machine shows error codes you cannot resolve.

Do not work on gas lines or high-voltage electrical yourself.

Verification

  • The machine completes a cycle with no sanitize error.
  • A sanitization test strip passes (or dishes reach required temp for high-temp machines).
  • No error codes. The booster heater or sanitizer system operates as expected.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify the dishwasher runs but fails sanitization; rule out fill or start problems.
  2. Water temperature Check incoming hot water temp meets the minimum for your machine type.
  3. High-temp — heater and thermostat Test booster heater and thermostat for continuity; replace if faulty.
  4. Low-temp — sanitizer Check sanitizer tank level and injector; refill or clear clogs.
  5. Call a pro Heater or thermostat faulty, gas smell, or repeated failures—call a commercial kitchen technician.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Machine type (high-temp or low-temp)
  • Incoming water temperature
  • Booster heater continuity (high-temp)
  • Thermostat continuity (high-temp)
  • Sanitizer tank level and injector status (low-temp)
  • Steps already tried

Does the dishwasher run but fail to sanitize?

Run a full cycle. Check for sanitize error, failed test strip, or dishes below required temp. If the machine does not fill or run, that is a different problem.

Run a full wash cycle. Check if the machine shows a sanitize error, fails a sanitization test strip, or dishes come out below required temp. Good: machine runs but sanitization fails. Bad: machine does not fill or run—see fix-dishwasher-will-not-fill or fix-dishwasher-will-not-start.

Yes No

You can change your answer later.

Is the machine high-temp or low-temp?

High-temp uses a booster heater for 180°F rinse. Low-temp uses chemical sanitizer. Check the machine label or manual.

Check the machine label or owner's manual. High-temp machine: booster heater for 180°F rinse. Low-temp machine: chemical sanitizer. Good: you know the type. Bad: unsure—call the manufacturer or a technician.

Known Unknown

You can change your answer later.

Is incoming water temp at least 120°F (high-temp) or 100°F (low-temp)?

Run hot water at the prep sink for one minute, then measure with a thermometer. High-temp needs 120°F minimum; low-temp needs 100°F or per manufacturer.

Run hot water at the nearest prep sink for one minute. Measure with a thermometer. High-temp: at least 120°F (49°C). Low-temp: 100°F (38°C) or per manufacturer. Good: temp meets minimum. Bad: water too cold—raise water heater or check hot water line.

Yes No

You can change your answer later.

Raise water heater and retest

Raise the water heater to at least 120°F for high-temp or 100°F for low-temp. Check that the hot water line to the dishwasher is not restricted. Retest a cycle. If it still fails, proceed to heater or sanitizer checks.

Done

High-temp or low-temp path?

High-temp: check booster heater and thermostat. Low-temp: check sanitizer tank and injector.

Choose based on your machine type. High-temp: proceed to booster heater check. Low-temp: proceed to sanitizer check.

High-temp Low-temp

You can change your answer later.

Does the booster heater have continuity?

The booster heater raises rinse water to 180°F. Test with a multimeter. No continuity means replace.

Unplug the machine and shut off water. Access the booster heater per your model. Test for continuity with a multimeter. No continuity: heater failed—replace with matching part. Continuity: heater good—check thermostat and rinse arm flow.

Yes No

You can change your answer later.

Replace booster heater and test

Replace the booster heater with a matching part (match the part number; commercial parts suppliers and the manufacturer sell replacements). Reassemble per your model. Restore power and water. Run a test cycle. If you smell gas near a gas-heated machine, shut it off and call a technician.

Done

Does the thermostat have continuity?

The high-limit thermostat can prevent the heater from running if faulty. Test at room temperature.

Locate the thermostat near the heater. Test for continuity at room temperature. If no continuity when it should be closed, replace it. If both heater and thermostat test good, check rinse arm flow for clogs. Reassemble and test.

Done

Is the sanitizer tank full and the injector clear?

Low-temp machines need chemical sanitizer. Empty tank or clogged injector prevents sanitization.

Check the sanitizer injector tank level—refill if empty. Locate the injector and inspect for clogs or mineral buildup. Clean or replace if blocked. Confirm the tubing is not kinked. Retest a cycle. Good: sanitizer flows. Bad: still fails—call a technician.
Question

Is the sanitizer tank full and the injector clear?

Done

Call a technician

Call a commercial kitchen technician if: the machine does not fill or run (different problem); the booster heater or thermostat tests faulty and you are not comfortable replacing them; you smell gas near a gas-heated machine; you have checked water temp and sanitizer and it still fails; or the machine shows error codes you cannot resolve. Do not work on gas lines or high-voltage electrical yourself.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a commercial dishwasher not sanitize?
High-temp machines: low incoming water temp, failed booster heater, faulty thermostat, or clogged rinse arms. Low-temp machines: empty sanitizer tank, clogged injector, or wrong chemical concentration. Check the machine type first.
Can I fix a commercial dishwasher that will not sanitize myself?
Yes, for many causes. You can check water temperature, refill sanitizer, clear injectors, and inspect rinse arms. Booster heater or thermostat replacement often requires a commercial kitchen technician—call a pro if you are not comfortable with electrical or plumbing.
When should I call a technician for sanitization failure?
Call a technician if the booster heater or thermostat tests faulty, you smell gas near a gas-heated machine, you have checked water temp and sanitizer and it still fails, or you are not comfortable working with high-temperature plumbing or electrical.

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