Commercial dishwashers should have a steady water pressure of 20-30 PSI for normal operations. If the water pressure is low, it will take longer to fill, it won’t clean the dishes well enough, and there may also be unusual pump noises. Find out the causes of low water pressure in your commercial dishwasher by following this guide and consult a commercial kitchen appliance repair professional for help.
Causes Of Low Water Pressure In Your Commercial Dishwasher
Partially Closed Water Supply Valve
You should begin by checking the supply valve. If the water pressure is low, it can be due to a partially closed supply valve. This can happen if someone’s cleaned the area or recently opened or closed the valve and forgot to do it properly.
Simply close the valve and open it again. If the issue persists, the valve could be faulty. But first you should check if other appliances are receiving enough water or not. If other appliances are also having low water pressure, the issue could be the water supply or the supply valve. But if other appliances are receiving regular water pressure, the problem may be somewhere near or in the dishwasher.
Clogged Spray Arm Nozzles
The spray arms in a commercial dishwasher are precision-engineered components designed to distribute water at highly specific angles and pressures to ensure complete coverage of dishware. Over time, the tiny nozzles on these arms become severely clogged by a combination of hard water limescale and food particulates.
When water is heated inside the dishwasher, calcium and magnesium bicarbonates precipitate out of the solution and form a hard, chalky calcium carbonate scale. This scale gradually narrows the diameter of the spray nozzles.
Additionally, if the wash tank’s primary filters fail to catch all the food soil, small items like celery strings, corn kernels, or napkin fibers can get jammed in the holes. When the nozzles are blocked, the water cannot escape the spray arms efficiently. This creates a physical bottleneck, causing the water pressure inside the arms to drop significantly.
As a result, the spray pattern becomes weak and irregular, failing to reach the upper racks or properly blast food off the dishes, which ultimately leads to failed health inspections due to inadequate sanitization. So, maintain your commercial appliances, including cleaning and descaling.
Blocked Water Inlet Strainer
Located right at the point where the building’s water supply line connects to the commercial dishwasher, there is typically a small, cone-shaped mesh screen known as the inlet strainer or water filter.
Its primary purpose is to catch municipal pipe debris—such as rust flakes, sand, solder particles, and small rocks—before they can enter the delicate internal components of the machine. In a busy commercial environment, or in older buildings with degrading iron or galvanized steel pipes, this strainer can become completely clogged in a matter of weeks.
When the strainer is blocked, it acts as a massive flow restrictor. Even if the city water pressure is perfectly normal at the street, the water struggles to pass through the clogged mesh, resulting in a severe pressure drop by the time it reaches the internal valves.
Because this screen is often hidden behind a brass fitting, it is frequently overlooked during routine cleaning, leading operators to mistakenly believe the dishwasher itself is broken when a simple five-minute screen cleaning would resolve the pressure issue entirely.
A blocked water filter or strainer can be the cause of a malfunctioning combi oven as well, so check the filter or strainer before consulting a commercial oven repair Fairfax Station expert.
Failing Fill Solenoid Valve
The fill solenoid valve is an electromechanical gatekeeper that controls the flow of water into the dishwasher. When the machine’s control board sends an electrical current to the solenoid, a magnetic coil lifts a plunger, which opens a rubber diaphragm to allow water to rush in. If this valve begins to fail, it will not open fully, creating a severe restriction that drastically lowers water pressure.
There are several ways this valve fails. First, the rubber diaphragm can warp, swell, or become brittle from years of exposure to hot water and harsh chemicals. Second, hard water scale can build up inside the brass body of the valve, physically preventing the diaphragm from lifting completely. Third, the electromagnetic coil itself can degrade, losing its magnetic strength and failing to pull the plunger with adequate force.
When the solenoid is only partially open, water is forced through a tiny gap, resulting in a massive drop in both flow volume and dynamic pressure, which starves the wash pump and prolongs the machine’s fill cycles. So, an expert will suggest replacing the fill solenoid valve.
Worn Wash Pump Impeller or Failing Pump Motor
The wash pump is the absolute heart of the commercial dishwasher’s hydraulic system. Usually driven by a heavy-duty electric motor, the pump utilizes an impeller—a rotating disc with curved blades—to forcefully push water through the plumbing and out of the spray arms.
Over years of continuous daily use in a harsh, hot, and chemical environment, the pump components inevitably wear out. The impeller can become eroded by cavitation, or its blades can be chipped by foreign objects (like broken glass or utensils) that slip past the strainers. In some cases, the internal connection between the motor shaft and the impeller strips out, causing the impeller to slip rather than spin at full speed.
When the impeller is damaged or slipping, it can no longer efficiently impart kinetic energy to the water. The motor might sound like it is running at full speed, but the hydraulic pressure generated will be severely compromised. This internal mechanical failure directly translates to weak, anemic spray arms that cannot properly clean or rinse the dishware.
Limescale Buildup In the Booster Heater
High-temperature commercial dishwashers are required by health codes to deliver a final rinse at a minimum of 180°F (82°C) to achieve chemical sanitization. Because standard building hot water tanks generally only heat water to around 120°F to 140°F, commercial dishwashers use an internal “booster heater” to rapidly increase the temperature of the incoming rinse water.
Because this heater deals with water being pushed to its boiling point, it is highly susceptible to rapid limescale accumulation. As hard water flows through the narrow coils or tank of the booster heater, the extreme heat forces calcium carbonate out of the solution almost instantly.
This scale coats the interior walls of the booster’s plumbing, effectively shrinking the diameter of the pipes.
As the pipe diameter decreases, friction increases exponentially, and the water pressure exiting the booster heater drops dramatically. This is a particularly dangerous cause of low pressure because it directly affects the final rinse cycle; if the pressure is too low, the 180°F water won’t reach all the dishes, violating sanitization requirements.
Conclusion
A low water pressure can severely restrict the operation of your commercial dishwasher. So, you should look for the above common problems. But it’s best to call in a commercial dishwasher repair Chantilly expert who will check everything and fix the problem.
