Troubleshooting Erratic Pressure, Loss of Pressure, and Low Water Volume in Pressure Washers

Troubleshoot erratic pressure, loss of pressure, or low water volume on Generac pressure washers by checking water supply flow and hose condition, cleaning the inlet filter and nozzle, and verifying settings. The article also explains triplex pump callouts (A through F) and includes an updated procedure to purge air from the pump, including turning the water back on fully before restarting for reliable operation.

Apr 3, 2026
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Troubleshooting Erratic Pressure, Loss of Pressure, and Low Water Volume in Pressure Washers

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Troubleshooting-Erratic-Pressure-Loss-of-Pressure-and-Low-Water-Volume-in-Pressure-Washers

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Read the owner’s manual thoroughly and understand all instructions, cautions, and warnings before using this equipment. If any section of the manual is not understood, contact your nearest authorized dealer, contact Generac Customer Support at 1-888-436-3722 (1-888-GENERAC), or visit Generac.com with questions or concerns.

Troubleshooting erratic pressure, loss of pressure, and low water volume in pressure washers

Many issues with no or low water pressure can be resolved by following the steps below.

1. Check the water supply. Ensure the spigot is fully open to allow maximum flow.
2. Allow water to run for 30 seconds prior to connecting.
3. Verify proper pressure and flow from the source. Flow must be greater than 3.8 gallons per minute and no less than 30 PSI.
4. Do not use one-way valves, vacuum breakers, or check valves in any part of the water supply.
5. Purge the system of air prior to using the pressure washer. See Purging air from the pump below.
6. Check both hoses for kinks or obstructions.
7. Confirm the water supply hose length does not exceed the 50-foot maximum length.
8. Check the inlet water filter (screen). Without the filter, debris can obstruct the pump and prevent adequate flow, resulting in erratic pressure or pump damage.
9. Ensure the correct nozzle is installed and the nozzle is clean. Use a needle or other pointed tool to clear the nozzle tip of any debris.
10. Ensure the spray gun is on the correct setting if using a PowerDial gun.
11. Ensure the throttle is set to high, if applicable.

If your pressure washer has a triplex pump (found on professional series pressure washers), confirm the adjustable unloader valve is set correctly:

Turn the pressure control knob counterclockwise (-) to decrease output pressure.
Turn the pressure control knob clockwise (+) to increase output pressure.

Triplex pump component callouts (A through F)

Triplex pump component callouts (A through F):

A: Pump oil fill cap or dipstick (location may vary by model).
B: Water inlet connection (garden hose connection).
C: Inlet filter or inlet port area (inspect the inlet screen for debris).
D: Adjustable unloader valve pressure control knob.
E: Unloader valve assembly (routes water when the spray gun trigger is released).
F: High-pressure outlet connection (to the high-pressure hose).

Note: All residential series pressure washers feature an axial cam pump with an unloader valve that is not field adjustable. If it is determined that a pressure issue originates in the pump or unloader valve itself, contact an Independent Authorized Generac Dealer using the dealer locator.

Purging air from the pump

If the steps above are completed and pressure is still fluctuating, there may be air trapped in the pump. To purge the pump of air, follow the steps below.

1. With the pressure washer turned off, ensure the supply hose (usually a garden hose) is connected and the water supply is turned off.
2. Trigger the spray gun to discharge any water and air that may be trapped in the system.
3. Turn on the water source and allow water to run through the pump for 20 to 30 seconds.
4. Turn off the water supply, then trigger the spray gun until all water and air is discharged. Before restarting the pressure washer, turn the water supply back on fully. Then start the pressure washer and test for steady pressure.

Failed pressure sensor

The OneWash (discontinued) featured a low water pressure sensor. If the sensor detected low water pressure, the machine shut off. Current pressure washer models do not have this sensor.