Dishwashers and Warewashing

A dishwasher that runs but does not sanitise looks identical to one that works. This is the distinguishing feature of warewashing equipment: the failure is silent, and it is exactly what an inspector tests.

The two types

High-temperature machines sanitise with heat. The final rinse must reach a specified temperature at the manifold, commonly around 180°F, with a corresponding temperature at the dish surface. They require a booster heater.

Low-temperature machines sanitise chemically, usually with chlorine, at a specified concentration. They run cooler and depend entirely on chemical delivery.

Each fails differently and each has a different daily check.

How they fail

Booster heater failure on high-temperature machines. The machine runs, the wash looks normal, the rinse does not reach temperature, nothing is sanitised. This is the classic silent failure.

Chemical delivery failure on low-temperature machines. An empty container, a failed pump, a blocked or perished tube. Same silent result.

Scale. As with ice machines and combi ovens, hard water scales heating elements, spray arms and jets. Reduced performance, longer cycles, eventual failure.

Blocked spray arms and jets. Food debris and scale. Produces poor wash results, which staff compensate for by re-running items rather than reporting.

Wash and rinse pumps.

Door seals and switches.

Drain problems, which are frequent and frequently plumbing rather than machine.

Water supply issues — pressure, temperature, or a failed incoming valve.

The daily checks that matter

These are food safety checks and they are also the earliest maintenance signal.

High-temperature machines: verify final rinse temperature every day, with a thermometer or a test strip designed for the purpose. Record it. Machines have gauges and gauges drift; independent verification is the point.

Low-temperature machines: test sanitiser concentration with test strips, every day, and record it. Check the chemical container level.

Both: check spray arms rotate freely and jets are clear. Check the door seal. Check the drain.

The record is the compliance evidence. An inspection asking for sanitiser logs is asking for something you either have or do not.

Water treatment

Scale is the primary long-term failure driver and it is preventable.

In hard water areas, treatment is required rather than advisable. Untreated machines in hard water need descaling frequently and fail early.

Descaling is a defined procedure with appropriate chemicals, done at intervals set by water quality and volume.

Chemical systems

Most operators use a chemical supplier who provides dispensing equipment as part of the supply agreement.

Know what that agreement covers. Frequently the dispensing equipment is the supplier's and they service it. Operators pay for repairs to equipment they do not own, or fail to call the supplier who would have fixed it free.

Chemical dispensing faults are a food safety issue, and the supplier usually treats them as urgent. Use that.

Concentration matters in both directions. Too little does not sanitise; too much is a chemical hazard and wastes money.

Preventive tasks

Quarterly or semi-annual, by a technician:

Descale. Clean and inspect spray arms and jets. Verify wash and rinse temperatures against calibrated instruments. Test the booster heater. Inspect pumps and seals. Check the drain. Verify chemical dispensing rates. Inspect the door and its safety switch.

Daily, by staff:

Temperature or concentration verification with a record. Clean filters and scrap trays. Check spray arms. Clean the interior at close.

Weekly:

Deglaze or delime according to the machine's requirement.

The symptom that gets ignored

"Dishes are coming out wet." Frequently the first sign of a rinse temperature problem, because hot dishes flash-dry and cool ones do not.

Staff treat it as a nuisance and towel-dry, which both defeats sanitising and hides the fault. It is worth telling kitchen teams explicitly that wet dishes are a reportable symptom rather than an inconvenience.

Capacity

Undersized machines produce recurring complaints that look like faults. A machine running continuously through service, with staff waiting, is at capacity.

The consequence is corner-cutting: shortened cycles, overloaded racks, insufficient pre-scraping. Each degrades the sanitising result.

Where a site consistently struggles, the answer is capacity or workflow rather than another service call.

The three-sink fallback

Every kitchen needs a documented manual procedure for when the dishwasher fails, and most have never practised it.

Three compartments: wash, rinse, sanitise. Where a three-compartment sink is not available, the site may not be able to operate.

Wash at the temperature specified locally, with detergent, scraping first.

Rinse in clean water.

Sanitise either by chemical at the correct concentration for the correct contact time, or by hot water immersion at the specified temperature for the specified duration.

Air dry. Towel drying defeats sanitising and it is the step staff revert to under pressure.

Test strips are required for the chemical method, and a thermometer for the hot water method.

Write the procedure down, with the numbers, and post it. A kitchen improvising this during a Saturday service will get the contact time wrong, and the failure is invisible.