How to Clean a Pressure Washer Filter

Cleaning a pressure washer filter takes about five minutes: switch the machine off, disconnect the hose, pull the small mesh screen out of the water inlet, rinse it under a running tap until the mesh is clear, then push it back in the right way round. Do it every few uses and you will avoid most of the pressure problems people blame on a dying pump.

Where the filter actually is

Nearly every domestic pressure washer has a small cylindrical or conical mesh screen inside the water inlet, the threaded connector where your garden hose screws on. On most Karcher, Nilfisk and Bosch machines it is a short plastic-framed gauze basket sitting maybe 15mm deep. Some models hide it behind a removable coupling you unscrew by hand.

That inlet screen is the one that matters and the one that clogs. Two others are worth knowing about: the detergent pickup filter, a foam or mesh piece on the end of the siphon tube or in the base of the tank, and an inline hose filter if you have fitted one at the tap end.

What you need

Long-nose pliers or tweezers to grip the screen, running water, and an old toothbrush. White vinegar is useful in hard water areas, and a torch helps you check the mesh is genuinely clear before it goes back in.

Step by step

1. Shut everything down. Turn the machine off at the switch, unplug it from the mains, and turn off the tap. Squeeze the trigger for a couple of seconds to release the pressure still trapped in the lance and hose. Skipping this step is how people get a face full of water.
2. Disconnect the garden hose from the inlet connector. Have a bucket or towel ready because there will be a small amount of water in there.
3. Remove the screen. Look into the inlet. On most machines the mesh basket lifts straight out if you grip the rim with pliers and pull gently while twisting slightly. If yours sits behind a screw-on coupling, unscrew the coupling first. Do not lever against the plastic threads, they are softer than they look.
4. Inspect it in good light. You are looking for grit, sand, rust flakes and general silt. A slightly grey screen is fine. One you cannot see daylight through is your pressure problem.
5. Rinse it from the inside out. Hold it under a tap so water flows the opposite way to normal, pushing debris back out of the mesh rather than driving it deeper. Work the toothbrush over the outside as you go.
6. Deal with limescale. If the mesh has a chalky white crust, soak it in a 50:50 mix of white vinegar and warm water for 20 to 30 minutes, then brush and rinse again.
7. Refit it the right way round. Most conical screens go in point outwards, towards the hose. Push it fully home so it seats flat, then reconnect the coupling.
8. Purge the air. Reconnect the hose, turn the tap on, and run water through with the trigger held open and the motor off until a steady stream comes out of the lance. Then start the machine.

Cleaning the detergent filter

If detergent has stopped drawing, the pickup filter is the first thing to check. Pull the siphon tube out of the bottle or lift the mesh basket from the tank, then rinse it in warm water. Dried detergent sets into a gel that will not shift under a cold tap, so soak it in hot water for a few minutes and squeeze it through instead. Flushing clean water through the detergent system after every use stops it happening at all.

When a filter is past cleaning

Screens are cheap consumables. Replace rather than clean if you see torn mesh, a cracked frame, or a screen deformed enough that it no longer seats flat. Any of those lets grit through to the pump, which is a far more expensive thing to damage. Replacement screens are typically a couple of pounds if you measure the diameter and depth first.

How often to do it

For occasional home use, check the screen every three or four sessions and clean it whenever it looks dirty. Clean it every time if you draw from a water butt or any non-mains supply, because those carry far more sediment. It is also worth a check at the start of the season after winter storage. Machines on a suspect supply are much better off with an inline filter at the tap end, which is far easier to clean and takes most of the load off the built-in screen.

Symptoms that point at a blocked filter

A clogged inlet screen starves the pump, and starved pumps behave in recognisable ways: pressure that fades after the first minute or two, a pulsating spray, and the motor cycling on and off more than usual. If cleaning the screen does not fix it, work through the rest of the water path before suspecting the pump. A kinked hose, part-open tap, low flow rate, blocked nozzle and trapped air all look similar and are quicker to rule out.