Pressure washer is surging/pulsing

June 10, 2025

BISON Santy

Hello, I am Santy, the funder of bisonclean.com. I have been in cleaning machinery field for more than 5 years now, and the purpose of this article is to share with you the knowledge related to pressure washer from a Chinese supplier's perspective.

Have you ever been using your pressure washer when suddenly the water flow starts jumping or the engine seems to speed up and slow down on its own? This is known as “surging” or “pulsing”. Simply put, it means the pressure won’t be consistent and the cleaning job won’t be done effectively. But don’t worry – this is a common problem that many pressure washer users encounter.

In this article, we’ll help you understand why your pressure washer is surging and guide you through easy steps to fix it so you can get back to a smooth and powerful clean. BISON will also share tips for maintaining your pressure washer for optimal performance.

What is pressure washer surge or pulsation?

Pressure washer surge or pulsation refers to fluctuations in water pressure during operation. Instead of delivering a constant, steady stream of water, the washer alternates between high and low pressure. Imagine spraying with a hose that feels like it’s breathing—strong one moment, weak the next. This not only makes cleaning less effective but also puts stress on the machine’s components. When surging happens, you might notice the spray pattern changing, the machine pulsing in a steady rhythm, or hearing unusual noises like banging or knocking.

Leading causes of pressure washer surge/pulsation

The pressure washer consists of several key components working together. First, there is the engine or motor that powers the machine. Then, the pump draws water from the water inlet and presses it into the system. The unloading valve releases excess water when necessary to regulate the pressure. Finally, the water is discharged through the outlet and nozzle for cleaning.

Problems in any of these links will cause fluctuations/pulsations. The following are some common reasons:

Water supply issues

Pressure washer surging often starts with water supply problems. Insufficient water pressure from the source or using a hose that’s too long, narrow, or kinked can restrict flow, disrupting the washer’s ability to maintain consistent pressure. Air in the system, caused by leaks, loose connections, or running the washer without water, can also result in pulsing. Additionally, dirty or damaged inlet filters reduce water intake, further contributing to pressure fluctuations.

Pump problems

If the inlet filter is clogged, debris can enter the pump and disturb its function. Over time, pump components like seals, valves, and pistons may wear out or get damaged, leading to inconsistent performance. Low oil levels or overheating can also affect pump efficiency. In some cases, the thermal relief valve may open to prevent overheating, which creates temporary pressure drops.

Unloader valve issues

The unloader valve regulates pressure by redirecting water when the trigger is released. If this valve becomes stuck, dirty, or improperly adjusted, it can’t manage pressure effectively, causing surging or irregular water flow. A malfunctioning unloader valve or incorrect pressure setting can make the pressure washer cycle between high and low output.

Nozzle and spray tip problems

Clogs from dirt, debris, or mineral buildup in the nozzle can block water flow, leading to fluctuating pressure. Using the wrong size nozzle or one that’s worn out also results in an uneven spray pattern and inconsistent pressure. A clean, correctly sized nozzle is essential for smooth operation.

Engine or motor problems

For gas-powered models, engine issues like stale fuel, a dirty carburetor, a clogged fuel filter, or a fouled spark plug can cause the engine to surge. In electric models, faulty components such as a weak motor, broken switch, or electrical connection problems may cause the motor to cycle on and off, affecting pressure output.

BISON advises: If your pressure washer is surging, start with the simplest checks first – check the water supply, hose condition, nozzle, and filter. These are common causes of failure and are usually easy to fix. If these checks do not solve the problem, check more complex components such as the pump or unloading valve.

How to fix surging/pulsing on a pressure washer

Safety tips: Before performing any checks or repairs, always unplug your pressure washer or turn off the engine. Wear protective gloves and safety gear to protect your body from potential injury.

Step 1: Check the water supply

Avoid using the washer in known low-pressure areas and check hoses for kinks, cracks, or leaks – straighten hoses or replace them with shorter, wider hoses as needed. Check all hose connections are tight and leak-free. Clean all water inlet filters to remove debris that may be restricting water flow. To bleed air out of the system, remove the nozzles and run water through the washer for a minute or two.

Step 2: Inspect and clean the nozzle

Remove the nozzle and check for clogs or blockages. Use a cleaning tool, small wire, or brush to clear debris and flush it with clean water before reattaching. Try a different nozzle size if the pressure remains inconsistent, and ensure the nozzle matches the specifications of your machine. Replace any nozzles that are worn or damaged.

Step 3: Check the pump’s inlet filter

Locate the pump’s inlet filter and clean it if it appears dirty, as a clogged filter can cause surging. Consider testing the washer with a different hose or spray gun to determine if accessories are contributing to the problem.

Step 4: Look at the unloader valve

Inspect the unloader valve, which regulates pressure changes. Clean it carefully, referring to your user manual for guidance. If the pressure appears incorrect, adjust the settings according to the manufacturer’s instructions. If the valve is stuck, damaged, or faulty, it may require replacement with a model-compatible part. For more detailed adjustment methods, see “How to adjust pressure washer unloader valve“.

Step 5: Check pump oil and engine parts (gas models)

Verify that pump oil is at the appropriate level and replace it if it looks dirty or aged. Examine the spark plug and air filter, and clean or replace them if needed. Check the pump for signs of wear, including leaks or damaged seals, and replace faulty parts like seals or pistons based on the manufacturer’s guidelines. Lubricate the pump as recommended to ensure smooth operation.

Step 6: Check and maintain electrical components (electric models)

For electric pressure washers, inspect the motor for any irregular behavior. Examine the power switch and wiring for damage or wear, and replace any faulty electrical components as necessary.

Preventing your pressure washer from clogging

Water source test: Test the water source for lack of water and cleanliness before use. This will prevent air from entering the system and damaging the pump, and avoid the possibility of dirt clogging the filter and nozzle.
Prevent air from entering the system: Secure all hose connections tightly before use. Prime the pressure washer correctly, especially after storage or long periods without use. Regularly inspect hoses and connections for leaks.
Clean filters and nozzles regularly: Rinse the water inlet filter and spray tips after each use to keep water flowing smoothly. Inspect nozzles for clogs and clean with a nozzle cleaning tool or thin wire. Replace worn nozzles to maintain optimal performance.
Service the pump regularly: Lubricate the pump and seals according to manufacturer recommendations. Check for wear and replace damaged components promptly. Keep pump oil clean and at the correct level if applicable.
Maintain the unloader valve: Check, adjust, and clean the unloader valve as per manufacturer instructions. Replace it if damaged or worn out.
Use manufacturer-approved parts and accessories: Ensure nozzle sizes match machine specifications and replace worn parts with genuine or compatible components.
Perform regular system flushes: After each use, run clean water through the machine to clear detergent and debris. Periodically deep clean with a descaling solution to remove mineral buildup.
Store your pressure washer properly: Keep the machine and hoses in a dry, clean location off the ground to avoid rust and damage. Protect it from freezing temperatures to prevent damage to internal components.
Store hoses properly: Coil hoses loosely and hang them up when not in use to avoid kinks or sharp bends. Inspect hoses regularly for cracks or wear and replace them as necessary. Avoid using long or narrow hoses that restrict water flow.
Winterize your pressure washer: Drain all water from the machine and hoses before winter to prevent freezing damage.

Conclusion

There is nothing more satisfying than using a stable, powerful, and reliable pressure washer. By understanding common causes and applying the troubleshooting tips shared by BISON, you can reduce interruptions and keep your pressure washer running smoothly.

At BISON, we understand how frustrating pressure washer surging or pulsing can be. As a trusted supplier of high-quality pressure washers and replacement parts, we are committed to providing equipment that performs to its full potential.

When you’re ready for a new pressure washer or dependable replacement parts, explore our range of BISON products designed to make every cleaning job easier and more efficient.