Harley Ryland
A pressure washer that suddenly loses pressure, pulses, surges or just doesn't hit like it used to doesn't necessarily need a new pump.
There are several things that can cause low or inconsistent pressure, and some of the easiest problems to fix can look surprisingly similar to a failing pump.
Before tearing into the machine, troubleshoot it in order.
Start with the water going in. Then check the water coming out. After that, start blaming expensive things.
Rather watch us troubleshoot it?
Watch Clean 85 mechanic Logan walk through the common causes of pressure loss and what we check before condemning a pump.
1. Make Sure the Pressure Washer Is Getting Enough Water
Your pressure washer can't put out water the pump isn't receiving.
An inadequate water supply can cause low pressure, surging, chattering and inconsistent performance. Pressure-washer manufacturers specifically list insufficient water flow, restricted inlets and kinked supply hoses among the causes of low or erratic pressure.
Start with the basics:
- Open the water supply completely.
- Make sure the garden hose isn't kinked or crushed.
- Completely unroll the supply hose.
- Check the hose for leaks.
- Inspect and clean the pressure washer's inlet screen.
- Make sure the water source can actually supply the flow the machine requires.
The required supply depends on the machine, so check the manufacturer's specifications. Don't assume that because water comes out of the garden hose, there's enough flow to properly feed the pump.
A machine rated for higher GPM obviously needs a water source capable of keeping up with it.
Feeding a Pressure Washer From a Tank?
Tank-fed systems introduce another set of possible restrictions.
Check the tank valve, plumbing size, inlet fittings and filter or strainer. Make sure nothing is partially closed, clogged or collapsing under flow.
Some pressure washer pumps and configurations are much happier with a flooded or pressurized inlet than others, so don't assume every machine can simply suck water from a tank sitting beside it.
2. Get the Air Out of the System
Air trapped in the supply hose, pump or high-pressure hose can cause erratic operation.
Before starting the machine, connect the water supply, turn the water on and hold the trigger open to purge air from the system until you're getting a steady stream.
Simpson specifically recommends purging air from the supply and pressure-washer system when troubleshooting low pressure.
It's simple, free and takes almost no time.
Do it before you start taking shit apart.
3. Check the Pressure Washer Nozzle
The nozzle is one of the first things we'd inspect when a machine isn't producing the pressure it should.
A clogged nozzle restricts flow and can cause abnormal or pulsing pressure. A worn or incorrectly sized nozzle can also affect the machine's operating pressure. Generac specifically identifies an obstructed nozzle as a cause of erratic or lost pressure, while Simpson notes that incorrectly sized or worn nozzles can result in low-pressure operation.
Remove the nozzle and inspect the orifice.
If it's clogged, shut the machine down, relieve the pressure and clean the nozzle according to the manufacturer's instructions.
If it's worn, replace it.
And make sure it's actually the correct nozzle size for the machine's GPM and operating pressure.
That's important enough that we covered it separately in our Pressure Washer Nozzle Guide.
Don't Forget the Soap Nozzle
If the machine suddenly seems weak after changing tips, make sure you didn't leave a low-pressure soap nozzle installed.
That's not a pump failure.
That's Tuesday.
Manufacturers specifically list having a low-pressure nozzle installed as a possible cause when a machine appears unable to produce normal pressure.
4. Inspect the High-Pressure Hose, Gun and Lance
Now follow the high-pressure side of the system.
Look for:
- Water leaking from the hose
- Damaged hose sections
- Leaking quick-connect fittings
- Leaks around the gun
- Problems at the gun-to-lance connection
- Obstructions in the hose or lance
A leak doesn't need to look catastrophic to deserve attention.
Manufacturer troubleshooting guidance specifically includes leaking or obstructed high-pressure hoses and leaking spray guns among possible causes of low or erratic pressure.
5. Pay Attention to How It Is Losing Pressure
This is where troubleshooting gets more interesting.
Constantly low pressure is different from a machine that repeatedly builds pressure and loses it.
And both are different from a machine that works normally cold and starts acting up after running for a while.
Pay attention to the symptom:
Low pressure all the time: Start with water supply, nozzle sizing, leaks and restrictions.
Pulsing or surging: Look closely at supply restrictions, trapped air and nozzle restrictions before assuming an internal pump problem. Generac notes that a clogged or restricted nozzle can produce a pulsing sensation at the gun.
Engine bogs when you pull the trigger: Now the engine itself, nozzle sizing, pump loading or another mechanical issue may need investigation. Manufacturer troubleshooting documentation treats engine bogging under load separately from basic low-pressure symptoms.
Pressure gets worse as the machine runs: That's useful diagnostic information too. Note how long it takes and whether anything else changes as the machine warms up.
That information can save a technician a lot of guessing.
6. Check the Engine or Motor
A pump can't perform properly if the thing driving it isn't performing properly.
On a gasoline pressure washer, an engine that isn't maintaining proper operating speed under load can affect pressure-washer performance.
That can lead you into normal small-engine troubleshooting such as fuel, air filter, ignition and engine condition depending on the symptoms.
On an electric machine, power supply issues can also matter. Simpson notes that inadequate line voltage and electrical supply problems can contribute to low pressure or motor stalling on electric pressure washers.
At this point, you're moving beyond “there's a rock in my nozzle” and into actual equipment diagnosis.
7. The Unloader Valve May Be Involved
If the supply, nozzle, hose, gun and power source check out, the unloader becomes one of the components worth investigating.
The unloader controls how water moves through the system when the trigger is released, allowing the pump to enter bypass instead of continuing to build pressure against a closed gun.
A malfunctioning, sticking, worn or incorrectly adjusted unloader can create pressure problems.
But this is where we'd stop recommending random adjustments.
Don't start turning the unloader adjustment because a YouTube comment told you to.
The unloader works as part of the pressure-control system, and improper adjustment can create bigger problems than the one you're trying to solve.
If you have reached this point without identifying the problem, proper diagnosis is a better move than blindly twisting things.
8. When It Actually Might Be the Pump
Yes, pumps do fail.
Valves wear. Seals fail. Components get damaged. Pumps can suffer from freezing, inadequate water supply, overheating and ordinary wear.
But the pump shouldn't automatically receive the death sentence because the machine lost pressure.
By the time you're seriously considering an internal pump problem, you should already have checked:
water supply → inlet screen → trapped air → nozzle → hose → gun/lance → engine or motor → unloader/system controls
If those check out and the machine still has low or unstable pressure, you're getting into legitimate pump diagnosis.
That's when a service shop starts making considerably more sense.
Preventing Pressure Problems
Good operating habits won't prevent every failure, but they can eliminate a lot of unnecessary ones.
Keep the inlet screen clean. Use the correct nozzle size. Make sure the machine has an adequate water supply. Don't allow a pump to freeze with water trapped inside it.
And don't leave a pressure washer running in bypass indefinitely while you wander off to do something else. Water recirculating through the pump can heat up; Simpson specifically recommends shutting the machine down if it won't be used for more than about two minutes.
For longer storage, follow the manufacturer's winterization and pump-storage recommendations. Residual water that freezes can damage internal pump components.
The Bottom Line
When a pressure washer loses pressure, don't start by replacing the pump.
Start with the simple stuff.
Make sure it has enough water. Purge the air. Check the inlet screen. Inspect the nozzle. Look for leaks. Then work your way toward the engine, unloader and pump.
Troubleshooting in that order costs almost nothing and prevents a ten-minute problem from turning into an unnecessary pump replacement.
And if you've checked all of that and the machine still refuses to cooperate?
That's why pressure washer repair shops exist.
Still Losing Pressure?
Clean 85 services and repairs most commercial and industrial pressure washing equipment in Tuscaloosa, Alabama. If you've checked the basics and your machine still isn't running right, give us a call or bring it by and we'll determine whether it's equipment we can service.
Pressure Washer Service & Repair →
Not sure if we work on your machine? Give us a call at (205) 553-4041 before bringing it in.