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On a gas machine the answer is stale fuel, a low oil level or a fouled plug — in that order. On an electric it is a tripped GFCI, an undersized extension cord or a thermal cutout. Almost every no-start fault is one of those six, and every one of them is free to check. Before you touch anything else on a gas unit, do this: squeeze the wand trigger while you pull the recoil. A pump holding pressure makes the engine extremely hard to turn over, and a lot of "the starter has seized" turns out to be nothing more than that.
Gas machines: the order to work in
| Check | What you are looking for | Time |
|---|---|---|
| 1. Trigger held while pulling | Pump pressure making the recoil almost immovable | 10 sec |
| 2. Fuel valve and choke | Valve open; choke fully closed for a cold start | 20 sec |
| 3. Oil level | At the full mark — low-oil shutdown blocks any start | 2 min |
| 4. Fuel age | Anything over 30 days without stabiliser is suspect | 5 min |
| 5. Spark plug | Wet, black, oily or wrongly gapped | 10 min |
| 6. Air filter | Packed with dust or grass | 3 min |
| 7. Fuel cap vent | Vacuum lock — loosen the cap and retry | 1 min |
| 8. Carburetor bowl | Varnish, water, sediment in the bowl | 30 min |
The fuel problem, in detail
Pump gasoline in the United States is normally E10 — up to 10% ethanol — and ethanol draws moisture out of the air. Left in a tank, the blend oxidizes over a matter of weeks and deposits gums that varnish the very small passages inside a carburetor. Absorb enough water and it phase-separates, so a layer of water and ethanol settles at the bottom of the tank exactly where the fuel pickup sits.
The practical consequence is that a machine stored full of untreated fuel in October frequently will not start in April, and the fault is not the engine. If the fuel smells sour or like varnish rather than like gasoline, drain it, dispose of it at a household hazardous waste site, and refill with fresh. If the engine then starts and runs, you have your answer.
Preventing it costs nothing: either run the tank dry before storage, or add a fuel stabiliser at the last fill of the season and then run the engine for several minutes so treated fuel actually reaches the carburetor bowl. Treating the tank and shutting the engine off immediately leaves untreated fuel in the bowl, which is precisely where the varnish forms.
The low-oil shutdown nobody remembers
Nearly every small engine fitted to a pressure washer has a low-oil sensor that prevents the engine starting when the level is below a threshold. It does not warn you; it simply refuses. Because these engines sit on wheels and get parked on sloping driveways, the sensor is also position-sensitive — a machine that will not start on a slope will sometimes start immediately on level ground.
Check the oil on a level surface, with the machine cool, at the full mark rather than merely somewhere on the dipstick. This is a five-minute check that resolves a genuinely large share of no-start calls. What oil goes in, and the separate question of pump oil, is covered in what oil does a pressure washer take.
Spark, air and the plug
Pull the plug and look at it. A dry, light-tan tip is healthy. Wet and fuel-smelling means it is flooded — leave the plug out, hold the throttle open and pull the recoil half a dozen times to clear the cylinder, then refit a dry plug. Black and sooty means it has been running rich, usually from a clogged air filter. Oily means something more serious and is worth a shop visit.
Gap matters and is easy to get wrong. Most small engines used on pressure washers specify roughly 0.028 to 0.031 inches; check the plate or manual for yours rather than assuming, and set it with a feeler gauge rather than by eye. Plugs are a few dollars, so replacing rather than cleaning is usually the better use of an afternoon.
Starts, then dies
This is a different fault from a no-start, and the pattern tells you where to look.
| Pattern | Most likely cause | Test |
|---|---|---|
| Runs on full choke, dies when opened | Lean — blocked pilot jet, varnished carburetor | Clean or replace the carburetor |
| Runs 5–20 minutes then quits, restarts later | Blocked fuel cap vent pulling a vacuum | Loosen the cap 30 seconds and retry |
| Stumbles, surges, then dies | Water in the fuel, or a partly clogged fuel filter | Drain the carburetor bowl and inspect |
| Dies once hot, will not restart hot | Marginal oil level tripping the shutdown, or an ignition coil | Top the oil; if it recurs, suspect the coil |
| Only runs while you keep priming | Fuel not reaching the bowl | Check the valve, filter and fuel line |
The fuel cap test deserves a special mention because it is so quick and so often correct. If the engine runs for a while and then dies, and loosening the cap for half a minute lets it restart, the cap vent is blocked and the tank is pulling a vacuum against the fuel pickup. A new cap is a cheap part.
Electric machines
Electric pressure washers fail to start for an entirely different set of reasons, and three of them are not faults at all.
The GFCI. These machines pull 13 to 15 amps and are usually on a GFCI-protected outdoor circuit, which trips readily around water. Press reset at the outlet and check the breaker panel. Many machines also have a GFCI module built into the plug itself, with its own reset button — check that too.
The extension cord. A long or thin lead drops enough voltage that the motor hums and will not turn, or starts and immediately stalls. Manufacturers typically specify 12-gauge outdoor-rated cord and a maximum length in the region of 25 to 50 feet. Running a washer off a 100-foot 16-gauge household lead is a common and entirely self-inflicted failure.
The total-stop system. Most electrics only run the motor while the trigger is held. A machine that sits silent until you squeeze the wand is behaving exactly as designed, and a surprising number of "it will not turn on" reports are this.
The thermal cutout. A motor that has been working hard, especially in bypass with the trigger released, can overheat and shut itself down. Unplug it and give it 30 minutes. If it does this repeatedly, the machine is spending too long in bypass — squeeze the trigger periodically or shut it off between sections.
A failed start capacitor. If the motor hums but will not turn and the supply is confirmed good, this is the usual culprit. It is a repair rather than a check.
The seasonal fault: it turns over but produces nothing
If the engine or motor runs normally and there is simply no water, you have a different problem and the starting system is fine. The usual seasonal cause is a pump cracked by ice: water left in a pump through a hard freeze expands and splits the head, and the machine that worked in October delivers nothing in April. Draining the pump and running a few ounces of pump-saver antifreeze through it before storage prevents the entire failure mode. The full diagnostic sequence is in pressure washer no pressure, and realistic lifespans are in how long pressure washers last.
Safety while you are working on it
Carbon monoxide. A gas pressure washer must never be run inside a garage, shed, basement or any partly enclosed space, and not next to an open window or door. Small engines produce carbon monoxide fast enough to be lethal in minutes, and it is odourless. Testing an engine "just for a second" in a garage is how people are killed by these machines.
Fuel. Let the engine cool before refuelling, keep fuel away from any ignition source, and do not attempt to clear a fuel line with compressed air near a hot exhaust. Dispose of stale gasoline through a household hazardous waste program, never down a drain or onto the ground.
Stored pressure. Before disconnecting a hose or a fitting, shut everything down, close the water supply and squeeze the trigger until the wand stops discharging. A high-pressure jet can inject water and grit under the skin through a puncture that looks trivial and is a surgical emergency — a 2023 study in Hand using the CPSC's national injury surveillance system estimated 15,307 high-pressure injection hand injuries in US emergency departments between 2012 and 2021, roughly 90% of them involving pressure washers.
Spark plug lead. Pull the plug cap before turning the engine over by hand or working near the blade of the recoil, so it cannot fire.
Stopping it happening again
Three habits eliminate most of the faults on this page. Stabilise the fuel at the last fill of the season and run the engine long enough for treated fuel to reach the carburetor, or store the machine dry. Drain the pump and run pump-saver through it before the first freeze. And check the oil before every use rather than every season — on a machine that gets used four times a year, that is four checks and it prevents both the low-oil shutdown and the engine wear behind it.
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