Basics & Fixes

Two numbers, one calculation

A pressure washer is sold on PSI and it is judged on PSI, and that is mostly a marketing artefact. PSI is how hard the water hits — the force that breaks dirt loose. GPM is how much water arrives per minute — the volume that carries dirt away and rinses it off. You need both, and multiplying them gives the number professionals actually use: cleaning units.

Two thousand PSI at 1.2 GPM is 2,400 cleaning units. Eighteen hundred PSI at 2.0 GPM is 3,600. The second machine has a lower headline figure and will clean a driveway faster, while being considerably less likely to damage anything. That single comparison is the most useful thing on this site, and it is spelled out in PSI vs GPM explained with a table of what each combination is suited to.

If you only read one page in this hub, make it what PSI pressure washer do I need. It goes job by job — car, patio furniture, deck, siding, driveway, oil stains — and gives a pressure band and a nozzle for each.

The first hour is where damage happens

Almost all pressure washer damage is done by someone using a machine for the first time, with the stock nozzle, at close range, on something delicate. Three habits prevent nearly all of it. Start further away than feels necessary and move in. Test on an inconspicuous patch. Keep the nozzle moving, always.

Add two mechanical habits and you have also prevented most early machine failures: never run the pump dry, even for a few seconds, and squeeze the trigger to release pressure before disconnecting anything. How to set up a pressure washer is the first-time sequence in order, and the common mistakes page is the list of what goes wrong and why.

The safety page is short and genuinely worth the two minutes: a zero-degree nozzle at close range will cut skin, the gun kicks hard enough to unbalance you on a ladder, and electric machines and standing water need thinking about.

Most faults are one of five things

Pressure washers fail in boringly predictable ways. It will not start: fuel, spark, choke, or on an electric unit a tripped breaker or the thermal cutout. It runs but will not build pressure: air in the system, a blocked nozzle, a clogged inlet filter, a kinked hose, or insufficient supply water. It pulses: usually air or a partial blockage. Soap will not draw: almost always the wrong nozzle. It leaks: a perished O-ring.

That is nearly the complete list, and it is why won’t start and won’t build pressure are written as checklists in order of likelihood rather than as essays. Work down the list and you will usually find it in ten minutes.

The one maintenance job that matters

Freeze protection. Water left in a pump expands when it freezes and cracks the housing, and a cracked pump generally costs more than the machine is worth. One minute with a bottle of pump saver each autumn prevents it. That is winterizing, and it is the difference between a machine that lasts two seasons and one that lasts ten.

Everything else is light: the maintenance checklist is a few minutes before and after each use, plus pump oil on gas machines with a serviceable pump.

Where to go next

Once the numbers make sense, the buying decision gets much easier: the pressure washers hub is where to go. And if you have a specific surface in mind, surfaces and how-to has the method for each one.