Questions

Pounds per square inch — the pressure of the water leaving the nozzle, which is the force that breaks dirt loose. It is the figure every machine is advertised on and it is only half the story; the other half is flow. See PSI vs GPM explained.

Gallons per minute — how much water the machine delivers. Pressure breaks dirt loose; flow carries it away. Multiply the two and you get cleaning units, which track real cleaning speed much better than pressure alone. A 1,800 PSI machine at 2.0 GPM beats a 2,000 PSI machine at 1.2 GPM on a driveway, and is safer on everything else.

For a car, roughly 1,200 to 1,900. For furniture, decking and siding, 1,500 to 2,000 with a wide tip. For concrete, 2,000 and up. Almost every homeowner is well served between 1,600 and 2,500 PSI. The job-by-job version is in what PSI do I need.

Electric, unless you have a specific reason not to. Gas buys you roughly double the water flow and costs you fuel, oil changes, noise, weight and a pull start. The deciding question is how big your biggest flat area is and how often you will clean it — the full comparison.

Red is 0 degrees (a pencil jet, almost always the wrong choice), yellow 15, green 25, white 40, and black is the low-pressure soap tip. Wider angle means less force and more coverage. Most homeowner jobs are green or white. Full chart: nozzle colors.

Almost certainly the nozzle. A soap injector only draws detergent when the low-pressure black tip is fitted — with any other tip the venturi cannot pull. That single fact explains the overwhelming majority of these complaints. Checklist: soap injector not working.

For concrete, siding, fences and decks, yes — most of what looks like dirt is living growth, and pressure removes the top of it while chemistry removes all of it. For rinsing dust off a car or a patio, no. See the honest answer.

A round attachment with spinning nozzles that cleans a 11 to 15-inch disc of flat concrete evenly, instead of a two-inch stripe. If you have any flat concrete, it is the single most worthwhile accessory. Size it to your machine’s flow rate — how to check.

Yes, at low pressure with a wide tip and sensible distance. A pressure washer is best used for a pre-rinse and a foam application; the dirt still comes off with a soft mitt. Limits and method: what PSI to wash a car.

Roof shingles, electrical panels and meters, air conditioning fins, old mortar, lead-painted surfaces, windows and skylights at close range, anything with a failing seal, and people or pets. The full list with reasons: surfaces you should never pressure wash.

Yes, with low pressure, a wide tip and a proper house wash doing the cleaning. The real risk is not the siding surface, it is spraying upward under the laps and driving water into the wall cavity. Method: how to pressure wash siding.

On an electric: a tripped breaker, a thermal cutout that needs a cooling period, or an extension cord dropping voltage. On gas: stale fuel, the fuel valve, the choke, or the spark plug. In order of likelihood: won’t start.

Usually air in the system, a blocked nozzle, a clogged inlet filter, a kinked hose, or a supply tap that cannot keep up. Work through won’t build pressure and you will normally find it in ten minutes.

Two things. Running the pump dry, even for a few seconds. And water left in the pump over winter, which freezes, expands and cracks the housing — and a cracked pump usually costs more than the machine is worth. One bottle of pump saver prevents the second: winterizing.

There are two standards: 1/4-inch quick connect (push-on) and M22 threaded, and M22 comes in 14mm and 15mm variants that look identical. The practical answer is to convert everything to quick connect once with a cheap adapter set. Guide: quick connect.

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