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How to Tell If Pressure Washer Pump Is Bad

Are you planning your next pressure-washing project? Better get started early in the morning if you want to cover everything from the fence to the pool, siding, porch and deck.


With the field prepped and pressure washer plugged in, you stand in front of the fence and press the trigger. You hear a sputtering sound, water dribbles from the gun for a few seconds and then a light stream follows despite the green nozzle attached. You keep releasing and pressing the trigger but the pressure remains low.


What’s going on?


Well, there could be a number of problems but in our opinion, it’s most probably the pump, which begs the question ― how to tell if a pressure washer pump is bad?


That’s what we are here to discuss. Keep in mind ― when a part gets damaged, it directly affects the washer’s pump. If water coursing through the pump gets left in the system, it’s possible that the other parts might start to rust.


Let’s take a look at the two most common reasons behind the washer pump going bad:

Sun Joe SPX3000 2030 Max PSI 1.76 GPM 14.5-Amp Electric High Pressure Washer, Cleans Cars/Fences/Patios

Unloader Valve

The unloader valve is a mechanism that leads the water flow into the pump. Water runs through a loop as soon as the trigger is released. The valve then closes and water remains under pressure. Though water is still running through the system, it does not flow out the nozzle. The pressure steadily increases but does not go too high.


The design of the unloader valve is what keeps the water flow in check and the pressure under control. This allows you to maintain consistent spraying pressure when the trigger is pressed. Moreover, this keeps the pump running smoothly.


This entire system works on the basis of the piston head, which is located inside the unloader valve. The piston head shifts and diverts water flow when pressure inside the pump is increased. This happens when you release the trigger. This is why you should never leave the machine running idle for longer than 15 minutes.


When the engine stalls and you hear sputtering sounds coming from it, it’s the unloader valve that has gone bad due to the increase in pressure in the pump. The engine works overtime to start the pump, which increases the risk of it exploding.


The longer the piston takes to divert water flow, the more the pump is affected. All in all, you will have to replace the unloader valve and get the pump fixed to use the pressure washer again.

Sun Joe SPX3000 2030 Max PSI 1.76 GPM 14.5-Amp Electric High Pressure Washer, Cleans Cars/Fences/Patios


If you have a gas pressure washer, then the cause behind the pump going bad might be the carburetor. The carburetor is either clogged or has been damaged. This is the part that mixes fuel with air and injects gas into the ignition chamber.


The quality of the gasoline is what affects the pump. Using oil that has been left in the system for more than 30 days will not power the machine fully. As a result, the pressure will be low, which will impact the pump and build pressure inside it. You already know what happens when the pressure gets too high ― KABOOM.

Sun Joe SPX3000 2030 Max PSI 1.76 GPM 14.5-Amp Electric High Pressure Washer, Cleans Cars/Fences/Patios

Other Pump Problems


Pump cavitation refers to the problem when bubbles form in the line that connects the water tap to the pump. This happens when water supply is low and as a result, the water pump stalls. A great trick to solve this problem is to make sure that the water supply is higher in gallons per minute than written in the manual.



As said earlier, never let the machine run idle for longer than 15 minutes. You already know that this builds pressure in the pump. As the engine overheats, the pressure keeps climbing and this will not only reduce the life of the machine but also fry the parts.

Sun Joe SPX3000 2030 Max PSI 1.76 GPM 14.5-Amp Electric High Pressure Washer, Cleans Cars/Fences/Patios

Pressure Washer Problems

Following are two charts that outline different problems in both electric and gas pressure washers. These problems attack the pump causing it to lose power over time.


Electric Pressure Washer Problems
Problem Cause Solution
Machine Is Not Working Faulty motor Motor needs to be replaced
Faulty electrical outlet Check the main fuse
Worn out wire Return under warranty
Motor Stops Running When the Machine Is Sitting Idle Low voltage Make sure that he plug is connected to the right outlet that provides adequate voltage or else you risk frying the motor and damaging the pump


Gas Pressure Washer Problems
Problem Cause Solution
Engine Stops Running When the Machine Is Sitting Idle Dirty oil filter Replace oil filter
Low oil level Use a dip stick to see how much oil needs to be added
Engine Is Not Starting Faulty spark plug Replace the plug
No gas Make sure to fill with the right gas
Pressure build up Before turning on the water tap, press the trigger to release pressure
The choke is closed Check the manual to move the choke to the right position
Worn out spark plug wire Change spark plug wire
Engine’s Power Is Not Strong Enough Incorrect RPM Check the manual and adjust RPM
Dirty air filter Replace air filter
Oil Looks Milky Worn seals Replace seals
Broken piston Get the engine repaired through warranty
Oil Is Dripping From the Engine Worn seals Replace seals
Simpson Cleaning MSH3125 MegaShot Gas Pressure Washer Powered by Honda GC190, 3200 PSI at 2.5 GPM, black

Our Final Thoughts

The first four things you need to look at in a pressure washer to find out if the pump is damaged are the unloader valve, carburetor, ventilation and water supply force. No matter the cause, all the pressure falls on the pump… literally.


Any problem with the pump will damage the other parts slowly and prevent the machine from working. It always starts small like the motor might stall or stop working in the middle, the pressure might fluctuate every few seconds or the engine might overheat.


Now that you know where to look, you can refer to the manual to find out where a certain part is located and then repair or replace it.


About Chris

When Chris first bought a house, he quickly realized that he was now going to need to be a weekend handyman. Every project that he worked on, he kept realizing that he needed more and more DIY tools. Chris is also someone who likes to do a lot of research before making large purchases. Since he had already done most of the research, Chris decided to put the info that he accumulated about his favorite daily tools onto