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SIMPSON

Simpson 4200 PSI Gas Pressure Washer, 4.0 GPM Commercial Power Washer, Cold Water, Honda GX390 Engine, 50' Hose, Aluminum Series, 49-State Compliant (ALH4240)

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Availability: In Stock.
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Arrives Wednesday, Jun 17
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Style: 4200 PSI


Features

  • SIMPSON PRESSURE WASHER FOR PROFESSIONALS: The Simpson Aluminum Series gas power washer cleans decks, driveways, siding, fencing, equipment, and graffiti; The cold water machine is great for contractors; 49-State Compliant (Not for sale in California)
  • ENGINE & PUMP: HONDA GX390 engine starts easily & includes low-oil shutdown; 4200 PSI 4.0 GPM CAT triplex plunger pump includes thermal relief to prevent overheating; Advanced oil seal technology & ceramic coated pistons extend seal life
  • LONG HOSE REACH: The Simpson Monster series 50' dual-braided high-pressure hose resists kinks and abrasion; Non-marring polyurethane jacket helps protect finished surfaces; Threaded M22 pump/hose connection
  • EASY MOBILITY: 13" premium pneumatic tires roll smoothly over gravel, grass, and curbs; Balanced layout improves transport; Aircraft grade aluminum frame with powder-coated finish is easy to assemble and resists corrosion; 38" L x 23.5" W x 29" H; 133 lb
  • PRO PRESSURE WASHER ACCESSORIES: Five quick-connect pressure washer tips (0, 15, 25, 40, and soap nozzle) cover tasks from stripping paint to car cleaning; Professional QC spray gun with safety lock-out and 16" spray wand included

Description

The SIMPSON Aluminum Series pressure washer 4200 PSI at 4.0 GPM is great for construction, equipment upkeep, and facility and fleet maintenance cleaning. With a powerful HONDA GX390 engine, reliable CAT triplex pump, and ultra lightweight aircraft grade aluminum frame, this pressure washer is the optimum blend of maneuverability and performance. The ALH4240 also comes with a 50’ hose, ergonomic spray gun, and 5 Quick Connect nozzles. Designed to meet the rigorous demands of the cleaning professional, the SIMPSON Aluminum Series frame is crafted of 100% aircraft grade aluminum, making it lighter in weight than most steel frame pressure washer designs. Perfect for contractors who specialize in deck cleaning, wood restoration, paint preparation, graffiti removal and all other professional cleaning services. The SIMPSON Aluminum Series designed for optimum performance in the harshest environments. Easy-to- assemble and easy-to-start, the Aluminum Series power washer is great for contractors who specialize in deck cleaning, wood restoration, and all professional services. 10 Year Limited Frame Warranty, 5 Year Limited Pump Warranty, 3 Year Limited Engine Warranty. Includes: Pressure Washer, Hose, Gun, Wand, 5 Quick connect nozzle tips, Detergent siphon tube with filter, Engine Oil, Quick start set up guide, Owner's manual.

Brand: SIMPSON


Power Source: Gasoline


Color: Red


Item Weight: 124 Pounds


Hose Length: 50 Inches


Product Dimensions: 38"L x 23.5"W x 29"H


Tank Volume: 2.5 Gallons


Maximum Flow Rate: 4 Gallons Per Minute


Global Trade Identification Number: 45


Maximum Pressure: 4200 Pound per Square Inch


Item Weight: 124 Pounds


Hose Length: 50 Inches


Item Dimensions L x W x H: 38"L x 23.5"W x 29"H


Tank Volume: 2.5 Gallons


Wand Length: 31 Inches


Power Source: Gasoline


Maximum Flow Rate: 4 Gallons Per Minute


Maximum Pressure: 4200 Pound per Square Inch


Color: Red


Brand Name: SIMPSON


Model Number: ALH4240


Global Trade Identification Number: 45


UPC: 879399001345


Manufacturer Warranty Description: Warranty Details Engine - 3 Year Limited Commercial Warranty | Pump - 5 Year Limited Warranty | Frame - 1 Year Limited Warranty


Manufacturer Part Number: ALH4240


Included Components: Aluminum 4200PSI,4.0GPM,Gas GX390


Unit Count: 1.0 Count


Item Type Name: Gas Pressure Washer, 4.0 GPM Commercial Power Washer, Cold Water, Honda GX390 Engine, 50' Hose, Aluminum Series, 49-State Compliant (ALH3228-S)


Manufacturer: SIMPSON


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Wednesday, Jun 17

This item is non-returnable:

Non-returnable. Transportation of this item is subject to hazardous materials regulation

View our full returns policy here.

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Similar Products

Top Amazon Reviews

    • Powerful, easy to start
Style: 4200 PSI
Started first pull. And has started on the first pull every time. I can definitely tell a power difference between this one and my other pressure washer with the same specs. Everything on this just looks and feels professional and high quality. The Aluminum cart is the icing on the cake! The only thing I didn’t like was the wand and the hose. The wand is way too bulky and too much plastic. The hose is decent but not very flexible. They just didn’t match the pressure washer. I would suggest in Investing in a high quality wand and hose and use what it came with for spares. ... show more
Reviewed in the United States on May 25, 2026 by Billy Herring
    • Great machine in terrible packaging.
Style: 4200 PSI
Very powerful and well built machine. I am glad that I did not purchase a less powerful unit. I was disappointed with two things: 1: The shipping box does not indicate which end is up, so the delivery driver plopped it down on its side. The exhaust guard was damaged but fixable. There is very little padding inside the box, so I am sure this happens a lot. 2: the engine bolts came loose from the mounting plate during my first use. I thought it sounded a little rattle and then moved it and saw the nuts laying on the ground. Better licking hardware should come on every unit, but especially one claiming to be for commercial use. Overall, a very nice piece of equipment. ... show more
Reviewed in the United States on May 13, 2026 by Mary benson
    • Power & Durability to be my last power washer
Style: 4200 PSI
This is a powerful, commercial unit - which is what I wanted. Despite residential use, I have a lot of flat surfaces - cement, aluminum dock and wood decking. This device with a surface cleaner does a great job and powerful enough (4200 psi @ 4 gpm) to do it quickly. It is well built with good wheels, but it does weigh 133 lbs. Looks like it will last forever and uses a high quality pump which should last a very long time. ... show more
Reviewed in the United States on June 1, 2026 by jlw
    • Quality assurance issues and excessive vibration transfer to the end user in included hose.
Style: 4200 PSI
This review is for the Simpson ALH4240 4200 PSI pressure washer. I replaced a similarly powered washer with this unit. The unit arrived with no apparent shipping damage and all appeared new. The “issues”, starting with least severe first. 1. The nut nearest one of the tires, threading through a bolt to the engine platform was not adequately tightened, and the nut fell off during the first usage session. Luckily I noticed it on the ground. 2. The aluminum handle bar (near the “dashboard”) had several burrs and nicks, which need to be buffed down to avoid scratches / cuts / etc while moving the unit. 3. It seems the included hose is unsuitable, and Simpson should provide a suitable replacement. It’s extremely rigid due to the metal layer running the length of the hose. The biggest issue with this is a very large amount of mechanical vibration is transferred from the motor/pump directly to the end-user/operator. IT’S PAINFUL TO EVEN USE THIS FOR MORE THAN A FEW MINUTES. Repetitive stress injury in the wrist/arm seems a real potential, on top of reduced productivity. The amount of vibration is obvious if you put your foot lightly on the hose. “Fighting” the hose while moving around is an issue too. You need to test this and have a mechanical engineer address the issue. ... show more
Reviewed in the United States on April 24, 2026 by S
    • Great pressure washer
Style: 4200 PSI
Of course the Honda engine is very well built as is the aluminum frame. All Honda motors have a weird oil level check they should throw away the dipstick you just fill the oil to the bottom of the threads it's less confusing. Strong CAT pump wish I had a better place to coil the hose as it's super stiff but obviously well built ... show more
Reviewed in the United States on April 28, 2026 by Amazon Customer
    • This thing is a beast!
Style: 4200 PSI
I read a LOT of reviews here on Amazon and other online resources before deciding to make such a sizable investment in this 4200 PSI/4.0 GPM machine. This is not my first pressure washer, but my third actually. Each time I upgraded in both PSI and gallons per minute. This is my first pressure washer that is categorized as commercial use. Having finally taken the time to put this machine to the test, I can honestly say this thing has more than enough power to satisfy the average homeowner or DIY’er. As I said in the title: this thing is a beast! Mine arrived complete and undamaged. Other reviewers reported scratches and dents but that was not my experience at all. Assembly was quick and easy. My shipment contained a quart of Amsoil synthetic 10W-30 for the engine crankcase but I have seen other reviewers that got their oil in a plastic pouch. Once assembled, the crankcase filled with the supplied oil, and the fuel tank filled 1/2 way, I hooked up the garden hose and bled the air out for 30+ seconds as recommended. Set the throttle to half-way and closed the choke and gave the starter a quick pull and it fired right up on the first attempt. After allowing the engine to run at partial throttle with the trigger open to keep the water flowing and the pump cooled for a few minutes, I increased the engine speed to approximately 3/4 and started cleaning the concrete patio as my first project with this unit. The pressure even at less than wide open on the Honda GX390 was more than enough to get the accumulated grime blasted off effortlessly. Next up, I connected my 15” surface cleaner which really sped up the process. The 4240 pressure and water flow are a perfect match for the Karcher 15” surface cleaner. With all of the positive attributes of this machine, there is one thing that I feel is a negative: the hose. It’s more than long enough for most jobs but the stiffness makes moving around with it a real challenge. Given the higher than average PSI capabilities of the ALH-4240 it’s not surprising that the pressure hose is more on the stiff side, but as others have commented, it would be a good idea to upgrade to a better hose. Honestly, at this price point, a better quality hose should come with it. Overall, the ALH-4240 is a great pressure washer that has all of the power that the average person could want for DIY use. The high PSI and GPM make short work out of even the toughest cleaning projects. Time will tell if it lives up to the Simpson advertised claims of dependability and reliability. ... show more
Reviewed in the United States on September 17, 2024 by Kenneth B.
    • Great product and support form Simpson
Style: 4200 PSI
Simpson did a fantastic job in their design of the aluminum model (ALH4240) of the 4200 PSI pressure washer. The weight difference is quite amazing. The listing does not mention, and Amazon's AI states that the engine is not aluminum. However, I can say with certainty that the Honda engine block is in fact aluminum. My only complaints are packaging and delivery. Simpson could do a much better job of securing the PW and accessories in the box. The unit was loose in the box with no packing. Instead, when Amazon delivered it (Upside down), the main unit and the accessories were all just sitting in the box loosely. Because of this, and the fact that it was dropped off upside down, the unit was sitting awkwardly on the detached aluminum handle, crushing one of the ends. I reached out to Simpson, where they very quickly took care of me by sending a new handle. It should be here any day now. ... show more
Reviewed in the United States on May 3, 2026 by Erik Drake
    • Impressive Pressure Washer
Style: 4200 PSI
This is an impressive machine. I bought the model with the Honda motor and CAT pump, this will clean just about anything! I bought it as an upgrade to an electric pressure washer, and this is a major upgrade! More power than I need for most jobs around the house, but it's good to have it if needed. My next project will be removing polysand from the joints of 960 sq.ft. of patio pavers. This thing will get a workout! My only feedback for improvement is the quick start guide did not flow from one page to the next correctly. It has several languages within and you have to search though the entire thing for your next steps, flipping it upside down or even going backwards to find the next steps. At least they were numbered, but I feel as though theu could do much better. Other than that, this pressure washer will not disappoint! Great product! ... show more
Reviewed in the United States on April 29, 2026 by Jason C. Blanton

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