Commercial dish machines sanitize by heat or by chemical. These answers cover the temperatures and concentrations the FDA Food Code requires for each, and how to verify them. Primary source: U.S. Food and Drug Administration.
The technical answers here reflect these published codes and standards, which your local authority (AHJ) adopts, amends, and enforces — educational, not engineering or legal advice. Confirm the current requirements for your jurisdiction.
It depends on machine type. In a high-temperature (hot-water) machine, the sanitizing rinse must be hot enough to raise the utensil surface to at least 160 degrees F (71 degrees C), per FDA Food Code 4-703.11. The fresh hot-water sanitizing rinse as it enters the manifold generally must be at least 180 degrees F for most machines, or at least 165 degrees F for a stationary-rack, single-temperature machine, and no more than 194 degrees F, under FDA Food Code 4-501.112.
A high-temp machine sanitizes with heat: a very hot final rinse that brings the dish surface to at least 160 degrees F (FDA Food Code 4-703.11). A low-temp machine sanitizes chemically, injecting a sanitizer such as chlorine into a cooler rinse. High-temp machines usually need a booster heater and dry dishes faster, while low-temp machines use less energy but depend on maintaining correct sanitizer concentration and buying sanitizer. Both are acceptable when operated to the Food Code requirements for their method.
Confirm the utensil surface reaches 160 degrees F, not just the machine's gauge reading. FDA Food Code 4-703.11 specifies verifying the 160 degrees F surface temperature with an irreversible registering temperature indicator, such as a heat-sensitive test strip or a maximum-registering thermometer run through the machine on a rack. The built-in wash and rinse gauges help monitor the machine, but the definitive check is the temperature actually achieved on the ware, because a hot gauge does not guarantee a hot dish surface.
A low-temp machine most commonly uses chlorine, and FDA Food Code 4-501.114 sets the parameters. For a mechanical chlorine sanitizing rinse, the solution must meet the code's minimum concentration, temperature, and pH conditions; chlorine is frequently run in roughly the 50 to 100 ppm range, but you must follow the specific values in the Food Code and on the sanitizer label. Verify the concentration at the final rinse with the correct test strips (required under FDA Food Code 4-302.14), not by assumption.
For a high-temp machine, you verify with a temperature indicator rather than sanitizer test strips, using the irreversible 160 degrees F surface check described in FDA Food Code 4-703.11. For a low-temp chemical machine, you do need the appropriate sanitizer test strips to confirm concentration at the final rinse. In both cases, FDA Food Code 4-302.14 requires the establishment to have a means to accurately measure the sanitization method in use, whether that means temperature or chemical concentration.
Common causes include a booster heater that is not reaching temperature, low incoming water pressure, clogged or worn spray arms, depleted sanitizer in a low-temp machine, or overloaded racks that shield surfaces from the rinse. Because FDA Food Code 4-703.11 requires the dish surface itself to reach 160 degrees F (high-temp) or receive the correct sanitizer concentration (low-temp), a machine that appears to run normally can still fail. Test the outcome with a temperature indicator or test strips and service the machine if it falls short.