Why a Gas-Powered Pressure Washer Won’t Start

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A pressure washer can clean lots of outdoor surfaces, but it's not much good if it won't start. Here's how to get it up and running again.

A pressure washer can be a great tool for improving the appearance of your home. It’s a terrific time- and back-saving piece of power equipment for cleaning a patio, garage floor, deck, driveway, walkway, fence, vinyl siding or even a boat. And let’s be honest: Using a pressure washer makes a day of mundane and exhausting cleaning almost fun!

What’s not fun, however, is discovering your pressure washer refuses to start. If this happens to you, all is not lost. Here’s a list of possible causes and how to get your gas-powered pressure washer running again.

Series:unrecognizable Worker Filling A Power Washing Machine With GasolineJodi Jacobson/Getty ImagesPressure Washer Won’t Start: Stale Fuel

Gasoline that sits in your pressure washer for more than six months becomes oxidized and contaminated. Degraded gasoline loses volatility and octane, causing lack of combustion, poor engine performance or a failure to start.

Drain dirty or contaminated fuel, then clean and flush the fuel tank with carburetor cleaner. Fill the fuel tank with fresh gasoline and turn the fuel valve to the “on” or “open” position before starting. Also, add fuel stabilizer to help keep fuel fresh.

Safety notes: Work in a well-ventilated area. Make sure there are no open flames or sparks nearby. Don’t smoke. And be sure to keep an A-B-C fire extinguisher nearby. And contact your local recycler or fire department to learn how to properly dispose of old gasoline in your area.

Pressure Washer Won’t Start: Dirty or Clogged Carburetor

Degraded gasoline can turn into varnish, which gums up and corrodes the carburetor, restricting gas from entering the combustion chamber. A clogged air filter can also keep your pressure washer from starting.

Remove the air filter and flush the carburetor with carburetor cleaner to remove any built-up dirt or carbon residue. Use a toothbrush to get into tight corners. If that doesn’t work, you’ll have to rebuild or replace the carburetor.

Pressure washer carburetors are simple devices, and making repairs is usually a DIY undertaking. Depending on the year, make and model, plan to spend $25 to $100 to rebuild your carburetor. Replace the carburetor with a new one if it shows any signs of spalling (spalls are small metallic fragments) due to corrosion.

A new carburetor will cost $30 to $200. A small engine repair shop will charge between $50 and $150 for labor to install one.

Spark Plug Close UpDrbouz/Getty Images

Pressure Washer Won’t Start: Fouled or Defective Spark Plug

The spark plug ignites the air/fuel mixture. A dirty, cracked or defective spark plug will keep your pressure washer from firing up. Replace the spark plug, don’t clean it. Replacing the spark plug should be part of your annual maintenance routine.

Pressure Washer Won’t Start: Bad Ignition Coil

Similar to a car, the ignition coil (AKA magneto or armature) sends high voltage to the spark plug to ignite the air/fuel mixture. A spark plug saturated with gasoline usually means little or no spark to the spark plug.

Use an inexpensive spark tester to check the plug for spark. No spark means you’ll need to replace the ignition coil, which you can do yourself.

Remove the coil wire from the spark plug, then remove the engine cover. Disconnect the wires to the coil, then unbolt and remove the coil assembly. Reverse these steps to install the new coil.

After installing the new coil, set the air gap between the coil and flywheel. You can find air gap specifications (usually between .010 and .014 of an inch) under the engine cover or in the owner’s manual. Use a feeler gauge to set the air gap. In a pinch, you can use a business card or strips cut from a plastic milk jug.

Pressure Washer Won’t Start: Broken Flywheel Key

The soft metal flywheel key connects the crankshaft to the flywheel. It can wear out from use, or, like a shear bolt on a snowblower auger, it can break if your pressure washer hits a hard object. Replacing a flywheel key is a job for your local small engine repair shop.

Leaking Hose ConnectionAllkindza/Getty Images

Pressure Washer Won’t Start: Excessive Pump Pressure

Excessive water pressure built up in the pump assembly will make the starter pull cord difficult to pull. Pointing the spray gun away from you, gently pull the trigger to release the pressure. You may want to try holding the trigger down while pulling the starter cord to release pressure.

The Final Word

Never start or run your pressure washer without water flowing through the pump. Running a pump when dry can destroy it in a few seconds. Annual preventive maintenance and proper storage, including draining all the water out of the pump and flushing with pump anti-freeze/lubricant, will keep your pressure washer operating at peak condition.

Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, educator and freelance writer who has written about DYI car repairs and vehicle maintenance topics. His work has been featured in The Family Handyman, a Reader's Digest book and Classic Bike Rider magazine. He has been a career and technical educator for 25 years teaching automotive technology, as well as writing state, federal and organizational foundation grants. He also helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into career and technical education.