Pressure Washer Stalls When Trigger Is Pulled: How to Fix

Pressure washers are valuable tools for cleaning driveways, decks, vehicles, and more. They harness the power of high-pressure water streams to remove dirt, grime, and stains effectively. However, encountering issues like a pressure washer stalling when the trigger is pulled can be frustrating and hinder your cleaning efforts. Pressure Washer Stalls When Trigger Is Pulled: Reasons and How to Fix

But what causes pressure washer to stall when trigger is pulled?

Typically, when a pressure washer turns off as the trigger is engaged, it often points to a defective unloader valve. The unloader valve holds significant importance among the pressure washer components. Various factors such as obstructions affecting the piston motion, worn-out O-rings, a loosely-tensioned spring, incorrect unloader valve configuration, or a malfunctioning pressure washer trigger can all contribute to the issue of the pressure washer shutting off while attempting to activate it by pulling the trigger.

In this blog post, we’ll delve into the common reasons behind this problem and explore potential solutions to get your pressure washer back in top working condition.

1. Unloader Valve Problems

An unloader valve is a component commonly used in various types of pressure washers and air compressors. Its primary purpose is to relieve pressure within the system when the flow of fluid (water or air) is stopped. This prevents the pressure from building up to dangerous levels and helps protect the equipment and components from damage.

In a pressure washer, the unloader valve is typically situated between the high-pressure pump and the spray nozzle. When the trigger of the spray gun is released, the flow of pressurized water stops. Without an unloader valve, the pressure within the system could rise to levels that might damage the pump or other parts. The unloader valve allows excess water to bypass back to the inlet side of the pump, reducing the pressure to a safe level.

Solution: Clean the unloader valve and its components to ensure smooth operation. If the valve is severely worn or damaged, consider replacing it. Adjusting the unloader valve to the manufacturer’s specifications can also help prevent stalling.

Pressure Washer Stalls When Trigger Is Pulled

2. Faulty Piston

The pressure retention within the unloader valve is managed by the piston, making it a vital component. During the operation of the pressure washer, the piston undergoes reciprocal motion, shifting back and forth. When this oscillation ceases or encounters disruption, the pressure washer automatically powers down. To examine the piston closely, it must be extracted from the unloader valve.

The unloader valve relies significantly on the piston for its operation. Should the piston’s motion cease or be disrupted, pulling the trigger might result in the washer shutting off. If the piston is not functioning properly, it should be replaced.

3. Problems with the O-Rings

One of the more frequent problems associated with pressure washers turning off is related to the O-ring. Within the unloader valve, there are O-rings, also referred to as seals or washers. When these O-rings become worn, degrade, or tear, they lose their ability to effectively seal the pump. Consequently, the unloader pump itself will also malfunction.

Examine the O-rings for significant signs of wear, tear, or deterioration. If they are no longer suitable for use in the unloader valve, it’s crucial to promptly replace them. Ensure that the replacement O-ring is of the exact same size as the old one to prevent any further complications. When installing the new O-ring, make sure the oil pump is correctly positioned and seated.

4. Incorrect pressure setting of the unloader valve

Higher pressure settings restrict the engine’s capability once the trigger is released. This occurs because, at elevated settings, the unloader valve obstructs the water’s diversion in the loop towards the inlet, thus impeding pressure release. Consequently, pressure accumulates within the machinery, resulting in the stalling of the pressure washer. To prevent this pressure-related shutdown, it is imperative to adjust the settings so that the unloader valve can redirect water back to the inlet, effectively preventing the buildup of pressure that leads to the shutdown of the pressure washer.

The water redirection function of the unloader valve struggles to effectively operate under high-pressure settings. This leads to the accumulation of pressure within the machine, prompting the washer to deactivate when the trigger is pulled. To address this issue, it’s necessary to readjust the settings to enable the unloader valve to smoothly open and redirect water within the loop back to the inlet, subsequently alleviating the pressure.

Before proceeding with the adjustment of the unloader valve’s settings, ensure that the engine is up and running. In order to expel any trapped air from the washer, activate the outlet valve. Attain your desired pressure level by carefully tightening the unloader valve spring. As you make pressure adjustments, also manipulate the lock nuts accordingly. Once the desired pressure setting is achieved, release the trigger and securely place the lock nuts, spring, and washer back into their initial positions.

5. Faulty pressure washer trigger

Addressing the aforementioned issues might not necessarily resolve the concern of the pressure washer failing to operate when the trigger is engaged. There could be an underlying problem with the trigger mechanism itself. As a first step, consider testing an alternate trigger to determine if this is indeed the root cause. If it proves to be the issue, proceed to disassemble the trigger to identify any potential faults. If the problem cannot be rectified, consider replacing the trigger mechanism.

6. Insufficient Water Flow

One of the primary reasons your pressure washer might stall when the trigger is pulled is inadequate water flow. Pressure washers rely on a constant and consistent water supply to operate efficiently. If the water supply is insufficient, the pump can’t generate the necessary pressure, leading to stalling.

Solution: Check that your water source is delivering enough water at the required flow rate for your pressure washer. Ensure that the water inlet filter or screen is clean and free from debris, as a clogged filter can restrict water flow. Additionally, make sure the hose isn’t kinked or tangled, as this can limit water flow as well.

7. Air in the Pump

Air bubbles trapped within the pump can disrupt the pressure washer’s functioning, causing it to stall when the trigger is pulled. This often occurs after setting up the pressure washer or after running out of water during operation.

Solution: To eliminate air from the pump, follow these steps:

  • Turn off the pressure washer.
  • Disconnect the water supply.
  • Squeeze the trigger on the spray gun to release any trapped air.
  • Reconnect the water supply and ensure a consistent flow before restarting the pressure washer.

8. Pump Issues

The pump is the heart of the pressure washer, and any problems with it can lead to stalling. Common pump-related issues include clogs, worn-out seals, and damaged valves.

Solution: Inspect the pump for any visible debris or clogs. Clean the pump thoroughly if necessary. If the seals or valves are worn or damaged, they might need replacement. Consult your pressure washer’s manual for guidance on pump maintenance or seek professional assistance if needed.

9. Other Potential Culprits

If you’ve attempted all the preceding measures and continue to experience problems with your pressure washer, there are a couple of additional options to consider. Inspect the air filter; if it appears dirtier than usual, perform a thorough cleaning. Utilize alcohol to clean the spark plug on the equipment.

The carburetor may also be obstructed or not properly secured. If it’s loose, tighten it. If it’s soiled, empty the gas tank and proceed to clean the carburetor to determine if this resolves the issue.

Occasionally, problems might arise from the water inlet or the wand screens. Take a moment to examine these components and ensure they are in a satisfactory condition.

Pressure Washer Maintenance Checklist

Pressure Washer Stalls When Trigger Is Pulled: Reasons and How to Fix

Before Each Use:

Inspect Hoses and Connections

Carefully examine all hoses for any signs of damage, such as kinks, cracks, or fraying. Damaged hoses can lead to leaks or decreased water pressure. Thoroughly inspect the connections where hoses meet the pressure washer, gun/wand, and nozzles. Ensure they are securely fastened to prevent any leaks during operation. If you discover any issues with hoses or connections, replace them promptly to avoid potential hazards and maintain optimal performance.

Water Source Check

Before starting your pressure washer, confirm that the water source is providing a consistent flow of clean water. Inadequate water supply can cause the pump to run dry, leading to damage. Utilize a clean water source to prevent debris and contaminants from entering the pressure washer system. This will minimize the risk of clogs and blockages in the machine’s internal components.

Check Nozzles

Inspect the nozzle for any visible signs of wear, such as deformation or corrosion. Damaged nozzles can affect the spray pattern and pressure. Ensure that the nozzle is securely attached to the wand or gun. A loose nozzle can lead to pressure loss and an inconsistent spray pattern. Before connecting the nozzle, ensure it is clear of any dirt, debris, or dried detergent residue. A clogged nozzle can result in reduced pressure and uneven cleaning.

Fuel/Oil Check (if applicable)

If your pressure washer is powered by gasoline or has an engine, check the fuel and oil levels before each use. Running the machine with inadequate levels can lead to poor performance and potential damage. Follow the manufacturer’s guidelines for fuel and oil types and quantities. This ensures optimal engine operation and prolongs the life of the machine.

After Each Use

Flush the System

After completing your cleaning tasks, it’s important to flush the pressure washer system with clean water. This helps remove any residual detergent, dirt, or debris from the pump, hoses, and nozzles. Connect the water supply and run the pressure washer for a few minutes without the detergent injector engaged. This flushes out any remaining cleaning agents and prevents them from clogging the system.

Release Pressure

Before disconnecting any hoses or nozzles, release the pressure within the system by triggering the gun/wand. This step prevents sudden releases of pressure that could potentially lead to accidents or injuries.

Drain Remaining Fluids (if applicable)

If you anticipate not using the pressure washer for an extended period, it’s advisable to drain any remaining gasoline or other fluids from the machine. This prevents stale fuel or fluids from deteriorating and potentially causing problems when you next use the machine.

Store Properly

Optimal storage conditions contribute to the longevity of your pressure washer. Store it in a cool, dry place, away from direct sunlight and extreme temperatures. This safeguards the machine’s components and prolongs their lifespan.

Regular Maintenance (Monthly or as Needed)

Inspect O-rings and Seals

O-rings and seals are critical for preventing leaks and maintaining proper pressure. Regularly check these rubber components for signs of wear, cracking, or damage. Replace them if necessary to avoid leaks that can affect performance.

Clean Water Filter

If your pressure washer features a water filter or inlet screen, clean it regularly. Filters can become clogged with debris over time, reducing water flow and straining the pump. Cleaning the filter ensures optimal water intake and prevents potential damage to internal components.

Check Spark Plug (if applicable)

For pressure washers with gasoline engines, inspect the spark plug periodically. Remove it and examine its condition. Clean or replace the spark plug if it’s fouled or worn, as this directly affects engine ignition and overall performance.

Inspect Pump Oil Level (if applicable)

If your pressure washer has a pump that requires oil, check the oil level regularly according to the manufacturer’s recommendations. Maintaining the correct oil level ensures smooth pump operation and prevents overheating.

Examine Hoses and Wires

Routinely inspect all hoses for signs of wear, including cuts, abrasions, or bulges. Damaged hoses can compromise water flow and lead to leaks. Similarly, check power cords for any fraying or exposed wires that could pose safety risks.

Lubricate Moving Parts

Refer to the manufacturer’s instructions for lubrication points on your pressure washer. Proper lubrication of bearings, pivots, and other moving parts minimizes friction and wear, contributing to smoother operation and extended component life.

Yearly Maintenance

Consider scheduling a yearly professional servicing for your pressure washer. Trained technicians can perform in-depth inspections, address any underlying issues, and perform maintenance tasks that are beyond the scope of regular user maintenance.

By diligently following these maintenance steps, you can ensure that your pressure washer remains in optimal condition, delivering reliable performance and extending its overall lifespan. Always refer to your pressure washer’s user manual for specific instructions and guidelines tailored to your machine’s make and model.


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