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Pressure Washer Stalls When the Trigger Is Released

Pressure Washer Stalls When the Trigger Is Released

Pressure washers tend to be pretty dependable but one issue that comes up often is a tendency to stall when the trigger is released. There is a common cause for this and a simple fix.

If a pressure washer stalls when the trigger is released, this usually indicates a fault in the unloader valve. It is a simple process to remove and replace the unloader.

Below, you can find the steps that will guide you in troubleshooting any issues that might arise with your pressure washer’s unloader valve. 

What Is the Unloader Valve?

The unloader valve of a pressure washer is a mechanism located on the top of the pump system (source). Depending on your power washer model, you might be able to identify this because of the black handle above the valve. 

The main job of this mechanism is to divert the flow of water that enters the pump system. As you release the pressure washer’s trigger, the valve will redirect the water into a loop, allowing it to retain its pressure even as you discharge it through the nozzle.

Lastly, the unloader valve has the task of preventing the water from reaching dangerous or too low levels of pressure

Ultimately, if you can spray water out of your pressure washer constantly and powerfully, it is all thanks to the unloader valve! A problem with this mechanism will cause your pressure washer to stall when you release the trigger. 

In the sections below, we will guide you through all the steps to resolve any problem you might be experiencing with your unloader valve. However, if you are in a rush, you can check out the basics of this job in the video below:

How a pressure washer unloader valve works (with cut-away view)

Gather a Screwdriver and a Wrench

The first step for fixing your washer is to gather all the tools and materials you will need for a job well done. Even if you are not an expert DIYer or mechanic, you are likely to have all these tools stored around your house. 

So, start by collecting:

  • A wrench
  • A screwdriver
  • Grease to oil the parts of the valve after cleaning them
  • Alcohol to clean the parts

Unplug the Unloader Valve

To fix your pressure washer, start by locating the unloader valve. Often, this is located above the pump system and identifiable thanks to a black handle. 

Generally, most makers tend to leave the unloader valve and its bay visible and easily recognizable. However, this can vary depending on the model and manufacturer of your pressure washer. 

Once you have identified it, use the screwdriver to unplug it. To do so, you should identify a retaining pin that has the role of keeping the valve in place within its bay.

This should be a U-shape metal pin that runs through the valve and the bay socket. You can easily remove the metal pin with a screwdriver. 

Use a Lever to Pull the Unloader Valve Off

Once the pin of the unloader valve is off, you should remove it from its bay. The movement necessary for this step is pulling the valve off the structure that keeps it in place. However, it can often be challenging to do so with your hands, especially due to the reduced spaces. 

That is why you might decide to use the screwdriver as a lever. This simple movement will cause the valve to pop off its bay. Now you can analyze it more easily.

Check the Functioning of the Piston

Once you have removed the unloader valve, you will be able to analyze it properly. At one of the extremities of the mechanism, you should be able to identify a piston. This is the core of the valve and the primarily-responsible mechanism for the functioning of the valve itself (source). 

If the piston does not move backward and forward freely, you have found the washer’s malfunction. Indeed, if the piston is placed or impeded, this will cause the washer to shut off. 

To restore its ability to move freely, follow the steps below:

  1. Use a wrench to unscrew the nut that keeps the piston in place.
  2. Unplug both the spring and the piston from the valve.
  3. Clean the piston with alcohol (you can also use kerosene as an alternative, just make sure all the oils, grease, and dirt is removed).
  4. Use silicone grease to grease the piston and the spring.
  5. Put all parts back into place.

If now the valve’s piston moves freely, but the washer still stalls when the trigger is released, there are other checks you could proceed with. 

Check the Valve’s Setting

Unloader valves have the important role of controlling and stabilizing the pressure of the water released by your pressure washer. However, these valves are set up manually to control such pressure.

Therefore, if the valve is currently running on a setting that is too high, it might cause the pumps to build up pressure that cannot be easily released. In turn, this can cause the engine to stall. This can also happen if the setting is too low, and the water does not reach a minimum required pressure. 

Here are simple steps to regulate the valve’s settings:

  1. Ensure that the engine is running properly and the nozzle is the correct one for the pressure.
  2. Find the valve’s black adjusting knob.
  3. Use a pressure gauge and position it between the hose and the pump. Make sure you can see the gauge while triggering the washer and adjusting the valve’s knob.
  4. Regulate the adjusting knob. To do so, trigger the gun while tightening the knob. 
  5. Reach maximum pressure and then let go of the trigger. You should notice a spike in pressure between 6% and 9%. This is the spot you will want the adjusting knob to be on.

Check the O-Ring

Once the pressure settings and the piston are back in place and working, you should inspect the O-ring. These mechanisms are also known as seals or washers and have the function of sealing the oil pump. 

If they have deteriorated and don’t work properly, this can cause the washer to shut off. If you have noticed damages, the only thing to do is to buy a new piece and replace the O-ring.

Reinsert the Valve

If still out, reinsert the valve in the bay and secure it with its U-shaped metal pin. Test the pressure washer to check if now everything is working well. Even if it is, complete the checks below before using it again.

If you are still at a loss on this – I want to encourage you to wash this short YouTube video. They do a great job of walking you through this visually:

How to replace an unloader valve on your pressure washer pump

Conclude Your Inspection

Before washing your patio or veranda, you should do a few extra checks to ensure that your pressure washer does not need servicing. These include:

  • Check the functioning of the engine
  • Verify that the water inlet is in good shape and does not show any sign of deterioration
  • Check the air filters, especially if you have not used your pressure washer in a while
  • Use alcohol to keep the spark plug clean


Pressure washers are very sturdy machines that can be with you for many years to come. However, proper maintenance is essential to ensure proper functioning. 

If you have noticed your pressure washer stalls when the trigger is released, there likely is a problem with the unloader valve. Fixing these problems is possible, and you will only need a few tools.

You can purchase unloader valves for common brands of pressure washers online (link to Amazon).

Before heading over to the shop or buy a new washer, try to fix the unloader valve and check the engine, filters, and spark plug of your machine.

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