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HOW-TO GUIDEHow to Clear an Airlock From a Pressure Washer
An airlock is trapped air sitting inside the pump or hose where water should be, and it stops the pump from building any real pressure. The fix is almost always the same: kill the pressure, open the water supply fully, and let clean water push the air out through the lance with the trigger held open before you switch the motor back on. It takes about two minutes and needs no tools.
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Pressure washer pumps are designed to move water, not air. Water is effectively incompressible, so when the pistons push against it they generate pressure. Air just squashes and springs back, so the pump ends up doing nothing useful while the motor happily spins away.
Air gets in whenever the inlet side is opened up: connecting the hose for the first time in the season, swapping a fitting, running the tap at too low a flow rate, or drawing from a water butt. Once a bubble is in there it tends to stay, because the pump has no real ability to shove it out on its own.
How to tell it is an airlock and not something else
The classic signs are worth separating from other faults, because the fixes differ completely:
- The motor runs but almost no water comes out of the lance, or it dribbles.
- You get short bursts of pressure mixed with spitting and hissing.
- The machine sounds rougher and higher pitched than usual.
- It started right after you connected the hose, changed a fitting, or brought the machine out of winter storage.
If instead the pressure fades gradually during normal use, or the machine has been fine for weeks and slowly got worse, you are more likely looking at a blocked nozzle, a tired unloader valve, or a clogged inlet filter.
Clearing the airlock, step by step
- Switch the machine off at the socket. Do not try to purge air with the motor running. Running a pump dry or against trapped air is what wrecks seals.
- Turn the water supply on fully. Not half a turn. A restricted supply is a common cause of the airlock in the first place.
- Remove the nozzle or tip from the lance. An open lance gives the air an easy escape route. With a narrow tip fitted it struggles to get past.
- Squeeze and hold the trigger. With the motor still off, mains pressure alone will push water through the pump and out of the lance. Hold it for 30 to 60 seconds.
- Watch what comes out. You want a steady, quiet stream with no bubbles or spluttering. If it is still coughing, keep holding.
- Release the trigger, then start the motor. Let it run for a few seconds, then squeeze the trigger again. It should now build pressure straight away.
- Refit the nozzle and carry on as normal.
If your lance will not flow much with the motor off, disconnect the high pressure hose at the machine end instead and let water run from the pump outlet until it flows clean, then reconnect.
Quick Tip
Purge every time you set up. Connect the garden hose, turn the tap fully on, then squeeze the trigger with the machine switched off until water runs steady from the lance. Only then plug in and start. That one habit prevents almost every airlock and takes about 20 seconds.
When the airlock keeps coming back
A one off airlock is normal. One that returns every time you use the machine means air is being drawn in somewhere on the inlet side, and purging will only ever be a temporary patch.
Check the inlet filter
Almost every machine has a small mesh filter in the water inlet. When it silts up with grit the pump gets starved, cavitates, and effectively creates its own air pockets. Unscrew the inlet fitting, pull the filter out with pliers, rinse it under a tap and refit it. If it is torn, replace it rather than running without one.
Check every connection for air leaks
A joint can be perfectly watertight and still suck air in, because the inlet side runs under suction rather than pressure. Check the hose to tap connector, the quick release coupling at the machine, and any adaptors in between. Worn or missing O rings are the usual culprit and cost very little to replace.
Look at your water supply
Long, narrow or coiled hoses choke flow badly. Most pressure washers want somewhere around 8 to 10 litres per minute at the inlet, and a thin hose left on a reel may not deliver it. Uncoil it fully and keep the run short. If you can fill a 10 litre bucket from the hose end in under a minute, flow is probably fine.
Suction and water butt setups
Drawing from a butt or tank is where airlocks become a real nuisance, because there is no mains pressure to push the air out for you. Only do it if your machine is rated for suction, keep the lift short, use a rigid hose with a foot filter, and prime the hose fully before starting.
Things worth avoiding
Do not run the motor in repeated short bursts hoping the air clears itself. Each dry run heats the pump seals with no water to cool them, and that is how a minor annoyance turns into a pump replacement. Switch it off, sort the water side, then start again.
How long should it take to clear an airlock?
Usually under a minute of holding the trigger with the motor off and the nozzle removed. If two or three minutes of running mains water through has not produced a steady stream, the problem is more likely a blocked filter or nozzle than trapped air.
Can an airlock damage the pump?
The air itself does no harm, but running the motor against it does. Without water flowing through, the seals and pistons lose their cooling and lubrication, and they can be damaged within a couple of minutes. Purge with the motor switched off.
Why does my machine airlock after winter storage?
Because the pump was drained, so it is full of air by design. That is normal. Purge it as above before the first start of the season, and use pump protector fluid when you store it so the seals do not dry out.