Why Your Pressure Washer Stalls When Releasing the Trigger


Pressure washers stalling when the trigger is released is a fairly common problem, and it’s one that is easily fixed. So what is the cause of your pressure washer stalling?

If a pressure washer stalls when you release the trigger, it is most likely to be a fault with the unloader valve. Removing and replacing the unloader valve is a simple process. The piston inside the valve may be the cause of the issue, or it could be as simple as needing to replace the worn O-ring.

I’ll now guide you through the steps you need to take to locate the problem inside of your pressure washer so that it no longer stalls.

What is an unloader valve?

The unloader valve is used to divert the water that goes into the pump system. The valve directs the water into a loop when you release the trigger on the pressure washer, and this means that the water maintains its pressure when exiting through the nozzle.

The unloader valve also does another job as it prevents the water pressure from getting too high or from dropping too low. If there is a problem with the unloader valve, then the pressure washer will not work when you release the trigger.

The following steps will help you to solve any problems you might experience with the unloader valve on your pressure washer.

How to repair a pressure washer

To repair your pressure washer, you will need a few simple tools:

  • Alcohol for cleaning the parts with
  • Grease to oil the parts of the unloader valve
  • Wrench
  • Screwdriver

1. Unplug unloader valve

If you’re going to repair a pressure washer, the first thing you need to do is locate the unloader valve. This is usually quite easy to do as it is often found above the pump system and has a black handle that makes it easy to spot.

It can sometimes depend on the make of your pressure washer, but the unloader valve will usually be visible and easy to spot and recognize.

Once you’ve found the unloader valve, you need to use your screwdriver to unfasten it. A retaining pin is used to keep the unloader valve in its correct position.

It will be a metal pin that is U-shaped, which goes through the unloader valve and the bay socket where it is situated. Once you have found the pin, then you can remove it with the screwdriver.

2. Remove unloader valve

Once you have removed the retaining pin, the next thing you need to do is take the unloader valve out of the bay socket where it is situated. To do this you will need to pull it off the structure that was keeping it in place in the bay.

This can be quite hard to do with only your hands as there’s not much space in the area where the valve is. Therefore, the easiest way to remove it is to use something as a lever. The screwdriver is ideal for this job, and you should then be able to just pop the valve out of the bay.

3. Check the piston

Now that the unloader valve has been removed from its bay, you can inspect it much easier. If you look at the valve, you should be able to see a piston at one end. This piston is the main part of the valve, and it is essential that it works correctly as it’s responsible for the proper functioning of the valve.

As you inspect the piston, you should check to see if it moves backward and forwards freely. If it doesn’t, you have found the reason why your pressure washer isn’t working properly.

You can repair the piston by doing the following:

  1. First of all, you will need to use the wrench to remove the nut that has been keeping the piston in place.
  2. Next, you should remove the spring and piston from the unloader valve.
  3. Using the alcohol, clean the piston thoroughly. If you don’t have any alcohol, then you can use kerosene instead, so long as you make sure all of the dirt and grease is removed.
  4. Grease both the piston and the spring.
  5. Now you should be able to put all of the parts back together.

Sometimes the pressure washer may still not work properly, even though the piston is moving freely. If this happens, there are a few other things you can check.

4. Check the valve setting

The main role of the unloader valve is to control and maintain the pressure of the water, and they are usually set up to control the water pressure manually.

Too much pressure can build up if the setting of the valve is too high, causing the pump to not be able to release the pressure, which results in the engine stalling. It is also possible for the engine to stall if the valve is set too low as the water hasn’t reached the minimum amount of pressure that is required.

You can regulate the settings by doing the following:

  1. First of all, you need to make sure that you are using the correct nozzle on the pressure washer for the amount of pressure that you are intending to use. You should also make sure that the engine is working properly.
  2. Next, you need to find the knob that is used to adjust the unloader valve. This will usually be black.
  3. Now you should use a pressure gauge to check the pressure of the water. To do this, you should put it between the pump and the hose and ensure that you are able to see it while you release water from the pressure washer and adjust the setting on the valve.
  4. You will now need to regulate the valve by releasing water from the washer and tightening the valve’s adjuster knob.
  5. Once you have reached maximum pressure, you can release the trigger. The pressure should spike between 6% and 9%, and this is where you want the adjusting knob to be set.

5. Check the O-ring

If you have checked the pressure of the water, and the piston is working correctly but your pressure washer is still not working properly, then you should take a look at the O-ring. O-rings are also called seals, or sometimes washers, as they are used to seal the pump and prevent it from leaking.

Sometimes they can deteriorate and so don’t function correctly, which can cause the washer to stall. If the O-ring has deteriorated, you will need to buy a new one and replace it.

6. Reinsert the unloader valve

If you haven’t already done so, then you will need to return the unloader valve to its bay and secure the retaining pin. Once you have done that, you can see if the pressure washer is now working properly.

Even if the washer is now working properly, you should always do the following checks before using the pressure washer again.

7. Finish your inspection

Before using the pressure washer again, it is a good idea to check a few more things to make sure that it is in full working order and doesn’t need servicing.

  • You should always check that the engine is working correctly.
  • Check that the water inlet looks to be in good working order and doesn’t show any signs of wear and tear.
  • Check that the air filters are clean, especially if it’s a while since the pressure washer was used.
  • Clean the spark plug with alcohol.

Regular maintenance is vitally important to ensure that your pressure washer functions properly and continues to last you for years to come. If you need a new unloader valveOpens in a new tab., they are widely available to purchase on Amazon.

Thanks for reading!

Graham Walsh

I want to share everything I know about home improvement in order to help you. Whether you're a home enthusiast or an industry professional, I have the information that you need.

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