Last Updated on September 25, 2026 by Umar Farooq
A pressure washer spitting air is delivering air that got into the water somewhere upstream of the tip — and in most cases it got in at a joint you can reach with your fingers, or it never left after the last time you unscrewed something. The jet coughs, drops briefly to nothing, then resumes. Sometimes you can see the burst leave the nozzle as a puff of white.
Hardly anybody types “spitting air” and stops there. Watching what people actually write, the same fault turns up as spitting, sputtering, spits and sputters, coughing, popping, bursts of air, air bubbles in the spray, and — the phrase that shows up most often on forums — air in the line. All one complaint: the machine is handing you something that is not water.
The reason this page exists separately from the four others on this site that live near the inlet is a distinction worth thirty seconds of your time. Air arriving at the tip is not the same event as air being manufactured inside the pump, and the two have very different price tags.
Spitting Air Is Air Being Delivered, Not Air Being Made
The pump industry keeps these in separate boxes and gives them separate names, which is more than most pressure washer troubleshooting lists manage.
Air entrainment is air that was already in the stream before it reached the pump and is still in it afterwards. Pumps & Systems is direct about what that means mechanically: the bubbles “do not become liquid, and their energy is substantially less than that of the imploding bubbles of cavitation”, and as a result air entrainment “typically does not cause damage to the impellers or casing.” The bubble goes in, gets squeezed, comes out the far end and lands on your driveway.
Cavitation is the opposite journey. There the bubble is made inside the pump, out of the water itself, because the pressure fell below the point at which water boils — and then it implodes against metal on the pressure stroke. The same bubbles to look at. A completely different outcome.
So if you are watching air leave the nozzle, that air made it all the way through. That is genuinely good news, and it is what separates this fault from its neighbours:
- Air leaving the tip in visible bursts — this page. Something admitted air into the water path and the pump passed it on.
- A gravelly rattle from the pump head with a spray that keeps softening — the pump is generating vapour internally, and eroding valve seats while you listen to it. That is pressure washer cavitation, and it is the expensive one.
- A rhythm you feel through the lance while the jet still looks solid — a beat rather than a cough, with no visible air. That belongs to pressure washer pulsating.
- The supply hose visibly going soft and flat under demand — the atmosphere crushing a starved hose, covered on pressure washer inlet hose collapsing.
They share causes on the inlet side and they can happen at once, which is why most of what you find online blurs them together. What they do not share is the bill. Two of them are a washer and a minute. One of them is a pump.
Purge It Properly: No Nozzle, Trigger Open, Machine Off
This fixes most cases of spitting air and it costs nothing, so it goes first regardless of what you suspect. Purging is not a repair — it is a documented step in normal start-up. Hotsy’s operator manual lists it among the numbered things you do before you begin: “Hold wand firmly, release trigger of trigger gun and turn pump switch ON. Squeeze trigger of trigger gun and allow air to purge from system” (Hotsy 558 operator manual, 8.914-369.0).
Do it in two stages rather than one. Almost every version of this instruction online skips the first stage, which is the one that clears the machine itself.
Stage one — the pump on its own.
1. Engine or motor off. Not idling at the far end of the garden. Off.
2. Disconnect the high-pressure hose at the machine, so the pump’s outlet is open to the air.
3. Open the tap fully and let water run through the pump and out of that outlet for twenty to thirty seconds. Anything trapped in the pump head leaves here, without fifty feet of hose in its way.
Stage two — the hose and the gun.
4. Reconnect the high-pressure hose and the gun. Take the nozzle off the end of the lance. No orifice means no restriction, and air leaves far faster.
5. Hold the trigger fully open with the machine still off. Water runs at plain tap pressure, which looks unimpressive and is exactly right.
6. Wait for silence. Not for a count — wait for the spitting, gurgling and popping to stop and the flow to go smooth. On fifty feet of hose that takes about a minute. Ten seconds is a gesture rather than a purge.
7. Start the machine with the trigger still held open, and fit the nozzle afterwards.
If you use detergent through a siphon tube, purge that line too: drop the tube into clean water, fit the soap nozzle and run it until the line is full and clear. An injector line left half empty over winter is a reservoir of air sitting in the discharge path, waiting for its moment.
One adjacent fault, one sentence of separation: a machine that never builds pressure at all and never produces a steady stream however long you hold the trigger has failed to prime, which is a different diagnosis from this one. Spitting air means water is arriving — just in company.
The Suction-Side Leak That Never Drips a Drop
If the spitting comes back within seconds of a proper purge, air is getting in on purpose, and the reason it is so often missed is that a suction-side leak does not leak.
Everything between the tap and the pump chamber drops slightly below atmospheric pressure every time a plunger draws back. A gap in that stretch will not weep water outward, because the pressure gradient points the other way. It quietly admits air inward, and it stays perfectly dry doing it. There is nothing to find with a paper towel.
Pump manufacturers put this near the top of their own symptom tables rather than the bottom. Udor’s plunger pump troubleshooting guide lists “Air leak in inlet plumbing” as the third cause of low pressure, ahead of anything internal, and gives the remedy as “Disassemble, reseal and reassemble.” Its rough-running entry reads “Restricted inlet or air entering the inlet plumbing,” answered with “Proper size inlet plumbing; check for air tight seal at fittings and filter” (UDOR USA, plunger pump troubleshooting guide).
The same document sets the margin you are working inside. Udor specifies a maximum inlet vacuum of 6 inches of mercury, which is under 3 PSI. That is the pump’s entire suction budget, so a gap that would be beneath notice on a pressurised line is a significant one here.
Where to look, in the order that finds it fastest:
- The rubber washer inside the garden hose coupler at the machine inlet. The commonest single answer, it costs pennies, and it goes flat and shiny with age. A hose nut can be finger-tight against a dead washer and still draw air on every stroke.
- The inlet filter housing. On most machines the screen sits behind a plastic or brass fitting with a seal of its own. If that fitting has been out recently — and after a cleaning it has — it may not have gone back down far enough to seal.
- Every quick-connect between tap and pump. Aquastop and flow-stop couplers carry a spring-loaded mechanism and two more O-rings than a plain brass connector. Take the clever fittings out of the chain entirely and screw the hose straight onto the machine. If the spitting stops, you have found it without diagnosing anything.
- Y-splitters and tap timers. Two joints where there was one, both on the low-pressure side.
- A cracked plastic inlet elbow. Hairline cracks in moulded inlet fittings are common on machines stored full over a freeze, and a crack on the suction side admits air rather than spraying water, so you will never see it.
The honest test is subtraction, not inspection. Strip the water path back to one hose and one connector, purge again, then add one fitting at a time. It is slow and it is certain, and it beats the soapy-water trick, which depends on pressure pushing outward and is therefore watching the wrong direction.
A Supply That Runs Out Between One Stroke and the Next
The third cause is neither a leak nor trapped air. It is the supply genuinely running dry for a fraction of a second, over and over.
A pressure washer pump does not sip. Three plungers take turns, and each has thousandths of a second to fill a chamber. If the water is not there at that instant, the chamber takes whatever is. A tap half a turn short of fully open will fill a bucket convincingly and still leave the pump short at the moment that matters.
Drawing from a tank adds a second mechanism that almost nobody allows for. As the level falls toward the outlet, the moving water begins to spin above it and a vortex forms, and that vortex reaches down and feeds air into the line while the outlet is still comfortably submerged. Pumps & Systems calls vortexing “the most common source of undesired air introduced into pump systems” and puts it down to insufficient submergence. A barrel that behaved impeccably for ten minutes and starts coughing near the halfway mark is doing exactly this. Keep the outlet deep, keep the tank topped up, and if it has baffles, use them.
Two tells separate a supply problem from a leak. The first is timing: supply-driven spitting keeps time with something outside the machine — a well’s pressure switch cycling, a tank draining, somebody running a shower indoors. A leaking fitting keeps time with nothing. The second is that it responds to the tap within a couple of strokes. Open the supply all the way and a marginal setup often cleans itself up on the spot; a dead washer will not care what you do at the other end.
If what you actually need is the arithmetic — what your tap delivers against what the pump is rated to pass — that is a timed bucket and one division, and it lives on pressure washer not enough water supply. This page owns the symptom; that page owns the measurement.
Once the Soap Bucket Empties, the Injector Draws Air
Here is the cause nobody lists, and the only one on this page that is not a pump problem at all.
A downstream injector sits *after* the pump, on the high-pressure side. Fit the black soap nozzle, system pressure drops, and the resulting venturi draws detergent up the siphon tube and into the stream on its way to the gun. That is the whole trick, and it works beautifully right up until the thing at the bottom of the tube stops being liquid.
When the bucket empties, or the tube floats off the bottom, or the strainer breaks the surface as you drag the machine forward, the venturi carries on doing its job and draws air instead. Soap, soap, soap, sputter, then more soap as the tube settles back. It looks like a serious fault and it is a bucket.
Two things follow, and both are useful. The first is a diagnosis that takes ten seconds: if the spitting only happens with the soap nozzle fitted and never on the green or the white one, stop looking at the inlet entirely. The second is reassurance. This air enters downstream of the pump, so it never reaches the valves or the plungers, and nothing inside the machine is being harmed while it happens. Untidy, not costly.
The rest of the injector’s failure modes — including the dried-detergent blockage that stops it drawing anything at all — are on pressure washer soap dispenser not working. The version that belongs here is the one where it draws air with enthusiasm.
The Check Valve That Lets the Chamber Refill With Air
Last, and least likely, which is why it is last. Each plunger works between two small spring-loaded check valves: one admits water on the way back, one releases it on the way forward, and each is supposed to shut completely so water can only travel one way.
A valve that no longer seals turns a closed chamber into an open one. On the discharge side, pressurised water and any air in it can expand back into the chamber the moment the plunger reverses. On the inlet side, the chamber can push back up the supply line instead of forward through the hose. Either way the pump loses its ability to sweep a pocket of air out and be done with it, and that is the signature: a machine that purges cleanly, runs smoothly for a few seconds, then starts spitting again with every fitting tight and the tap wide open.
The manufacturer’s table lists the two culprits in a deliberate order. Udor gives “Fouled or dirty inlet or discharge valves” with the remedy “Clean inlet and discharge valve assemblies,” and only then “Worn inlet or discharge valves” and “Replace worn valves.” Dirty comes before worn, because one piece of grit under one sealing face is enough — and grit is a great deal cheaper to fix than wear. This is also the argument for the inlet screen that nobody looks at until something else has already failed.
A check valve jammed permanently open is a more dramatic fault than a valve that merely leaks, and it is not what this page covers. What belongs here is the sequence: purge, tighten, measure the supply, and only then take a valve stack out. If you reach the valves and they turn out clean and sealing, you have ruled out the expensive end of the list with a spanner instead of a credit card.
Two Percent Air Costs You Twelve Percent Pressure
Air in the water is not a cosmetic problem, and the pump trade has measured how quickly it bites. Pumps & Systems publishes the curve: “Air entrainment at 2 percent will reduce pump performance by up to 12 percent. At 4 percent, it will reduce pump performance by 40 percent and at 10 percent, it will likely stall the pump altogether.”
Be careful with those figures, and I will be careful with them too. They come from industrial pumping practice, not from a bench test on a 2,500 PSI plunger pump in somebody’s garage. What transfers is the shape: a small percentage of air by volume costs a disproportionate amount of performance, and it goes non-linear fast. The exact numbers for your machine are not published by anyone I could find, and I am not going to invent them.
The far end of that scale is worth taking seriously, though. Ten percent air stalls a pump; a hundred percent is running dry, and running dry is the one version of this fault that does real damage quickly. Udor lists “Running pump dry” among the causes of premature wet-end seal failure and answers it in capitals: “DO NOT run pump without fluid / Replace seals.” The seals depend on the water for cooling as much as for sealing, and there is nothing else in there to do that job.
Which brings me to the opinion, and it is aimed squarely at what gets sold as a cure for this. Nothing you can buy addresses the top of this list. Valve kits, unloaders, seal kits and replacement pumps all sit at the bottom of it, below the free minute and the tuppenny washer — and yet they are what a search for spitting air puts in front of you, because nobody makes money on a purge. Two pump manufacturers’ own troubleshooting tables rank air in the inlet plumbing above every internal component they sell. Take them at their word. Purge it properly, strip the fittings back to one hose and one connector, fit a fresh washer, measure your tap. If it still spits after all four, go shopping — and you will be shopping for the right thing, which is the entire point.
FAQ
Why is my pressure washer spitting air out of the nozzle?
Because air got into the water path and the pump passed it through. Five candidates, roughly in order: air left in the system after a hose change, a pump swap or winter storage; a loose inlet fitting or a dead hose washer drawing air on the suction side; the supply momentarily running out; a detergent siphon tube drawing air once the bucket empties; and an inlet or discharge check valve that no longer seals. The first is free to rule out, so start there.
How do I get air out of a pressure washer?
With the machine off, disconnect the high-pressure hose and let the tap run through the pump alone for twenty to thirty seconds. Reconnect the hose and gun, take the nozzle off the lance, and hold the trigger fully open until the flow goes smooth and silent — about a minute on fifty feet of hose. Then start the machine with the trigger still open, and fit the nozzle last.
Is air in a pressure washer bad for the pump?
Air that is simply passing through does less harm than most people fear, because air bubbles do not implode against metal the way vapour bubbles do. The risk lies in what the air implies: an inlet that admits air is often an inlet that cannot deliver enough water, and a starved pump cavitates, which does erode valve seats. Fix it promptly — but for the mechanism behind it rather than the air itself.
Why does my pressure washer spit air after changing the hose?
Because you opened the water path, let a hose full of air into it, and nothing has pushed that air out yet. A pressure washer has no automatic vent. Every time you disconnect the supply, swap a hose or wake the machine up after storage, the system needs purging before the engine starts. It is a normal start-up step in manufacturers’ own manuals, not a sign that anything is wrong.
Can a loose inlet fitting make a pressure washer spit air?
Yes, and it is the leak that catches people out, because it never drips. The inlet side falls below atmospheric pressure on every intake stroke, so a gap there pulls air inward rather than pushing water outward and the joint stays completely dry. Udor’s own troubleshooting table names an air leak in the inlet plumbing as a top-three cause of low pressure and tells you to reseal the joint.
Why does my pressure washer sputter only when I use soap?
Because the detergent siphon tube is drawing air instead of detergent. The bucket has emptied, the tube has floated off the bottom, or the strainer lifted clear as you moved the machine. A downstream injector sits after the pump, so that air never touches the valves — it goes straight out of the tip. If the sputter vanishes the moment you fit a high-pressure nozzle, that is your confirmation.
Is spitting air the same thing as cavitation?
No, and the difference is where the bubble was born. Spitting air is air that came in from outside, travelled through the pump and left through the nozzle. Cavitation is water vapour created inside the pump by low pressure, which collapses violently against the valve seats and takes metal with it. They share inlet-side causes and can occur together, but one is an inconvenience and the other is quietly machining your pump.
How long should I hold the trigger to purge a pressure washer?
Until the water runs smooth and quiet, which is a condition rather than a time. On a short hose that can be twenty seconds; on fifty feet with the nozzle still fitted it can run to several minutes. Take the nozzle off and it goes much faster. Most people stop at ten seconds, see the flow steady briefly, and start the engine on a system that is still half full of air.
One Free Minute Before You Spend Anything
The order that works here runs from free to expensive, and happens to run from outside the machine to inside it. Purge properly, in two stages. Strip the inlet back to one hose and one plain brass connector, with a fresh washer in it. Open the tap all the way and check what it actually delivers. Look in the bucket, if you were running soap. Only then start thinking about valves.
And if you have been standing there watching your machine cough at a wall, wondering whether the pump is finished — it probably is not. Air coming out of the tip is air that got all the way through, which means nothing inside has been chewing on it. Go and find the joint that let it in.
