my greenworks electric pressure washer is making a weird pulsating sound and the pressure goes up and down, is this normal?

Diagnosis

This phenomenon is known as "cavitation." It occurs when the pump is unable to draw a consistent volume of water to match the speed of the internal pistons. Instead of a solid stream of liquid, the pump is sucking in air pockets or "voids." When these air pockets hit the high-pressure valve, they collapse violently, creating that rhythmic, pulsating "thumping" sound and causing the spray pattern to fluctuate between a powerful jet and a weak drizzle.

This is almost never a mechanical failure of the motor itself, but rather a supply-side restriction. The GPW1804 requires a steady flow of water to maintain its 1800 PSI rating. If the water cannot enter the pump as fast as the pump is pushing it out, a vacuum forms in the intake line. You can confirm this by looking at the water entering the machine; if you see erratic surging or hear a "gurgling" sound coming from the intake hose, your pump is starving for water.

How to Fix It

To resolve cavitation and stabilize your pressure, follow these steps precisely to maximize your flow rate:

1. Maximize Source Flow: Fully open your outdoor spigot. Do not leave it half-open to "save water." The pump needs the maximum available gallons per minute (GPM) to prevent air pockets from forming.
2. Eliminate Hose Kinks: Walk the entire length of your garden hose. Even a slight "pinch" or a tight loop in the hose can restrict flow enough to cause the GPW1804 to pulse. Ensure the hose lays flat and straight from the faucet to the machine.
3. Purge Air from the System: Turn off the pressure washer. Disconnect the spray nozzle (wand) from the high-pressure hose. Turn the water spigot on and let the water run through the machine and out the open hose for 30-60 seconds. This flushes all trapped air bubbles out of the pump head before you apply the back-pressure of a nozzle.
4. Inspect the Inlet Filter: Unscrew the garden hose from the water inlet of the pressure washer. Look inside the female connector for the small mesh screen filter. If it is clogged with sediment, algae, or mineral buildup, use a toothbrush and vinegar to scrub it clean. A clogged filter is a primary cause of suction loss.
5. Check Connections: Ensure the hose clamps or twist-locks at the faucet and the machine are tight. A leak at the intake side can allow the pump to suck air into the line, even if water is still flowing.

If That Didn't Work

• Upgrade Your Hose Diameter: If you are using a standard 1/2-inch diameter hose, the GPW1804 may be starving. Switch to a heavy-duty 5/8-inch or 3/4-inch diameter hose. The larger internal diameter allows for a higher volume of water to reach the pump with less friction loss, which usually eliminates pulsating immediately.
• Shorten the Supply Line: If your garden hose is over 50 feet long, the pressure drop over that distance can lead to cavitation. Try using a shorter 25-foot hose to see if the pulsing stops. If it does, you know the issue is "friction loss" caused by the length of your line.
• Verify Water Pressure: If you are using a rain barrel or a low-pressure gravity feed, this machine will not work. The GPW1804 requires a pressurized municipal or well-water source. If your home water pressure is abnormally low (below 30 PSI), the pump cannot prime correctly.
• Check for Nozzle Clogs: Occasionally, a tiny piece of debris in the spray tip can create excessive back-pressure, making the pump struggle and sound like it is pulsating. Try swapping the nozzle for a different color/degree tip to see if the behavior changes.

Heads Up

• NEVER run the pump dry: Running the machine without water for even a few seconds can overheat the pump seals and permanently damage the internal pistons.
• Winterize the Unit: Always drain all water from the pump and hoses before storing for winter. Frozen water will crack the pump housing, which is not repairable.
• Use a GFCI Outlet: Always plug your GPW1804 into a Ground Fault Circuit Interrupter (GFCI) outlet to prevent electrical shock, as you are working with water and high-voltage electricity.
• Avoid Extension Cords: Using a thin, long extension cord can cause a voltage drop, which makes the motor run slower and can exacerbate the pulsating sound. Use a 12-gauge heavy-duty cord if necessary.