How to Troubleshoot Pressure Washer Problems Like a Mechanic

1 Here’s how we know what they are:
2 Summary Table of Troubleshooting Tips:
3 Instructions How To Correct The Tricky Issues
4 Everything You Need to Know About Removing the Unloader Valve to Check for Issues
5 The Difference Between Flow and Pressure Actuated Unloaders
6 Troubleshooting the Unloader Valve
7 Sources

Here’s how we know what they are:

Reading 300+ emails from pressure washer users asking for help to solve their machine’s issues and counting the occurrences of each fault in an Excel spreadsheet.
Going through 16 popular pressure washer brands’ Operating Manual and tabulating the troubleshooting sections’ listed problems and solutions.
Looking through my power washer logbooks over the last 8 years to see the most common issues.

After spending 14+ hours gathering the data the common faults could easily be broken down into 5 sections: Water pressure problems, water leaking issues, gas machine specific problems, electric pressure washer faults and other common problems. From there the troubleshooting tips are broken down to 3 columns: What’s wrong, most likely cause and how to fix.

Quick note: Always check your Operator’s Manual for troubleshooting tips and safety first. Be aware many of the problems have 5 or more possible solutions for you to try.

pressure washer troubleshooting

Summary Table of Troubleshooting Tips:

The goal of this entire page is to make the most useful pressure washer troubleshooting guide on the internet. We constantly update and improve this table. It was last updated July 11, 2023.

Water Pressure Problems
What’s Wrong?	Cause	How to Fix
1. Low pressure	Insufficient inlet water supply	Unkink garden hose, ensure full water pressure coming from tap, use large enough diameter garden hose (see manual)
	Blocked inlet water filter	Remove garden hose connection and remove debris
	None or incorrect nozzle	Ensure correct nozzle being used
2. No pressure	Damaged unloader valve	Adjust unloader screw, check for damaged seals/springs
2. No pressure	Damaged pump inlet valves/manifold	Disassemble pump and replace/clean components of inlet manifold
3. Pulsing pressure (high then low)	Damaged pump inlet valves/manifold	Disassemble pump and replace/clean components of inlet manifold
	Faulty pump	Replace pump
	Pump sucking air	Turn off machine (but not water supply) and release pressure by squeezing trigger gun
	Obstructed nozzle, water inlet filter or gun/spray wand	Use needle to clear nozzle, fresh water to flush water inlet and vinegar to clear any deposits in gun/wand
4. Spiking pressure	Poorly calibrated unloader valve	Adjust unloader to proper pressure as per manual
5. Pressure drops after a few seconds use	Nozzle blocked	Clear nozzle with needle
5. Pressure drops after a few seconds use	Issues with unloader valve	Remove unloader and clean/repair
6. Pressure washer isn’t cleaning the surface	Using wrong nozzle	Switch to higher pressure spray nozzle
Water Leaking
What’s Wrong?	Cause	How to Fix
7. Water leaking from pump	Seals broken, cracked or worn	Return and replace under warranty
	Loose bolts on pump assembly	Tighten bolts to ensure pump casing properly sealed together
	Thermal valve activated	Wait 5 minutes before using (it will de-activate once cool enough)
8. Water leaking from garden hose connection	Broken or improper connection	Connect properly
8. Water leaking from garden hose connection	Broken rubber washer	Replace
9. Water leaking from spray wand or connections	Broken o-ring inside hose connection	Replace o-ring or return hose for new
9. Water leaking from spray wand or connections	Not properly connected	Connect properly
Gas Power Washer Issues
What’s Wrong?	Cause	How to Fix
10. Engine will not start	No gas	Fill with gas
	Choke is wrong position	Move to correct position as per manual
	Pressure build up	Squeeze trigger gun to release pressure in system
	Spark plug wire not connected	Connect wire
	Faulty spark plug	Replace with new
11. Engine stops running while in use	Low oil level	Check and fill oil
11. Engine stops running while in use	Dirty air filter	Clean or replace it
12. Engine not providing enough power	Dirty air filter	Clean or replace
12. Engine not providing enough power	Engine not running at correct RPM	Adjust RPM to engine specs with pump detached
13. Oil dripping from engine	Worn seals	Replace seals (covered by warranty)
14. Water in oil – looks milky	Worn or broken pistons allowing water through	Repair engine through warranty
14. Water in oil – looks milky	Worn seals	Replace seals (covered by warranty)
Electric Pressure Washer Problems
What’s Wrong?	Cause	How to Fix
15. Machine won’t start	Electric outlet is faulty	Check main fuse, check plug
	Not plugged in	Plug in
	Faulty motor	Return under warranty
16. Motor stops running while in use	Low voltage	Check voltage is within motor specified range
Other Common Problems
What’s Wrong?	Cause	How to Fix
17. Chemical/detergent injector not working	Using wrong nozzle	Insert black soaping nozzle on wand
	Soap tube inlet filter clogged (hose end that sits in soap bottle)	Flush with fresh water
	Soap inlet valve is clogged or blocked (pump side of tube)	Remove hose and use small Allen key to push through hole to remove debris/unstick the ball valve
	Detergent mixture is too thick	Add more water to dilute
18. Irregular bypass causing pressure fluctuations (sometimes) after use	Worn or broken unloader valve seals, springs or other components	Remove and replace
	Unloader valve not properly installed	Remove and install correctly, properly seating the valve at the bottom of the pump housing
	Water leaking from unloader valve	Replace worn or broken seals and re-install unloader valve to specification
	Dirt in unloader	Remove and clean
19. Excessive noise	Water intake is blocked	Check and clean or replace
	Not enough oil in engine	Check and add oil
	Not enough oil in pump	Disassemble and check (if possible) and add oil, otherwise return under warranty
20. Oil leaking from pump	Loose bolts/fitting	Check and tighten
20. Oil leaking from pump	Damaged parts like seals or pistons	If comfortable disassemble to check, clean and replace, otherwise return under warranty

Instructions How To Correct The Tricky Issues

In this section are instructions how to fix the tricky pressure washer issues, namely the ones that require you to tear down the pump.

The Lazy Man’s Way to Diagnose Water Pressure (No Pressure) Issues

Here’s the 5 step approach to solving 95% of water pressure issues in 10 minutes or less:

Check water supply: Open the water supply valve to full to ensure the pump is getting enough flow.
Check hose for kinks: I can’t tell you how many times I’ve tested a pressure washer, got everything going, only to pull the trigger have it not reach pressure. I check the inlet for blocks. I check the nozzle. I check the water is on. And after all these things check out and it’s still not working I turn it off to read through the manual to find out what I’m doing wrong. Then, all of sudden, I notice a kink in the hose and realize how much an idiot I was not to notice. I fix the kink start the machine and it all works fine. Don’t make this mistake – always check for kinks.
Release air from system: Always connect the garden hose to the power washer first. Then turn the water tap on and pull the trigger gun to release water from the system at the garden hose water pressure before starting the engine or motor. This will release all the pressure from the system and allow the pump to function.
Ensure correct nozzle and nozzle not clogged:

Use a needle to clear the nozzle tip of any debris. Any blocks at the nozzle will cause decreased flow and increased pressure in the systems, possibly triggering the unloader to enter bypass.

Still experiencing water pressure problems? Okay, no worries, we’ll need to get the tools out to remove unloader valve and check for issues – see below.

Everything You Need to Know About Removing the Unloader Valve to Check for Issues

Unloader valves allow water to run through the pump when you are not holding down the trigger on the pressure gun. If there was no unloader valve then pressure would build inside the system (when not in use) so when you did pull the trigger it would stall the engine or explode a weak link part – probably the pressure hose o-ring.

Check out where the unloader is located on 3 different pressure washer pumps:

As you can see the unloader is located on the exit side of the pump because it allows the pressurized water to flow back through the pump when it isn’t exiting into the high pressure hose (you’re not pressure washing anything).

Take a look at two different disassembled unloader valve assemblies:

The one on the left is from the Stanley gas pressure washer also shown in the above image on the left. It is a flow actuated unloader.

The unloader on the right is from an AR Blue Clean electric pressure washer. It is a pressure actuated unloader.

Both these assemblies can be taken out of the pump for cleaning and repair, without damaging them.

The Difference Between Flow and Pressure Actuated Unloaders

Flow actuated – As the name suggests, these unloader valves respond to water flow stoppage. When there is no flow leaving the nozzle the valve will “open” allowing water to flow back to the pump inlet.

Pros: Safer because doesn’t require pressure build up.
Cons: More sensitive to system issues like a clogged nozzle, incorrect nozzle orifice size and other flow problems.

Pressure actuated – Instead of responding to flow, this type of unloader is forced open by an increase in water pressure allowing water to bypass back to pump inlet (this pressure is increase is usually caused by flow stoppage).

Pros: Less sensitive to flow issues within the system because it responds only to trapped pressure on the outlet side of the pump.
Cons: Less safe because it needs pressure rise to work (could cause failures within system).

Troubleshooting the Unloader Valve

Many pressure problems begin and end at the unloader. A cracked o-ring, dirt caught in the spring or a stuck shaft are the most common issues solved by simply removing the unloader and cleaning/looking for issues.