Common problems and repair guides for pressure washers
Pressure washers pair a small engine with an axial or triplex pump, and problems fall into two categories: engine issues (won't start, surges, stalls) and pump issues (no pressure, pulsating pressure, leaking). The pump side often needs unloader valve cleaning or pump oil replacement, while the engine side follows standard small engine diagnosis. Our pressure washer guides cover both for popular brands like Simpson, Generac, Honda, and Ryobi.
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Simpson Pressure Washer Cranks But Won't Start — Fuel & Spark Diagnosis
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This guide covers Simpson pressure washers that pull over or crank freely but won't fire. If the engine won't crank at all — the pull rope is locked solid or the electric starter doesn't spin — that's a different problem (often fuel hydrolocking the cylinder or a seized pump), not what's covered here. When it cranks but won't catch, the cause is almost always one of three things, in order: stale fuel that has gummed up the carburetor's tiny pilot jet, no spark from a failed ignition coil or sheared flywheel key, or a tripped low-oil sensor grounding out the ignition. Simpson pairs its pumps with several different engines — Honda GX/GC, Kohler, and Briggs & Stratton are the most common — so confirm which engine is on your unit before ordering parts. Start with fresh fuel and a spark test before opening the carburetor.
The most likely causes of a pressure washer having no pressure include a faulty pump, clogged nozzles, or air in the system. Start by checking for clogged nozzles and ensure that the pump is functioning correctly.
Pressure loss in Karcher units is most commonly caused by a restricted water inlet screen, a clogged nozzle, or a stuck unloader valve. First, verify your garden hose provides at least 5 GPM and clean the mesh inlet filter. If the motor runs smoothly but pressure drops when the trigger is pulled, inspect the unloader valve for calcium buildup or worn O-rings.
First, pull the trigger on the spray gun to release hydraulic head pressure, which often prevents the engine from reaching starting RPM. If it pulls easily but won't fire, spray a 2-second burst of carburetor cleaner into the air intake; if the engine pops or runs briefly, your carburetor's main jet is clogged. Ensure the oil level is exactly at the 'Full' mark, as low-oil sensors are the primary cause of 'no spark' on Honda GCV and Briggs & Stratton engines.
On a Honda GX200, the most common culprit is a triggered Low Oil Alert sensor or a clogged pilot jet inside the carburetor. First, check that the oil is filled to the very brink of the fill plug, as even a slightly low level will ground the ignition coil. If oil is full, verify fuel flow by draining the carburetor bowl and testing for spark using a dedicated tester to isolate the ignition system from the fuel system.
A surging pressure washer is most often caused by a restricted fuel flow or air entering the system, frequently due to a clogged carburetor or a dirty air filter. Start by checking your air filter and trying a fuel system cleaner to see if the idle stabilizes before moving to more involved repairs.
Most starting issues are caused by old gasoline, a dirty carburetor, or a fouled spark plug. Start by checking your fuel levels and ensuring the engine switch is in the correct position before moving to deeper engine components.
If your Ryobi pressure washer engine is cranking but won't fire, the most likely culprit is a clogged carburetor jet or a low-oil shutdown sensor preventing ignition. Perform a 'starting fluid test' by spraying carb cleaner directly into the air intake; if the engine fires for a second then dies, your problem is 100% fuel-delivery related. If it doesn't fire at all, you must check for a fouled spark plug or a sheared flywheel key that has moved the ignition timing.
An oil leak in a pressure washer pump is usually caused by worn-out oil seals or a damaged O-ring. Start by cleaning the unit to locate the exact source of the leak, then determine if a seal kit replacement can resolve the issue.
Low or no pressure in a Ryobi pressure washer is most often caused by a clogged spray nozzle or a stuck unloader valve. First, verify your garden hose isn't kinked and the inlet screen is clear, then purge air from the system by holding the trigger with the engine off. If pressure doesn't return, the unloader valve is likely seized in the bypass position and needs to be cleaned or replaced.
The most frequent reason a Ryobi pressure washer won't start is stale gasoline clogging the carburetor. Start by checking your fuel quality, ensuring the spark plug wire is connected, and confirming the fuel valve is in the open position.
Pressure loss is typically caused by a mismatch in water supply flow (GPM), a partially clogged or worn-out nozzle tip, or a malfunctioning unloader valve that is bypassing water prematurely. Check your inlet screen for debris and ensure your garden hose provides at least 1 GPM more than the pump's rating to prevent cavitation. If the engine runs fine but pressure is low, focus entirely on the pump's internal check valves and the unloader settings.
Most-needed maintenance items to keep your equipment running.
Pump oil degrades — change annually to prevent pump failure.
Find on AmazonWorn nozzles lose pressure — a fresh set restores cleaning power.
Find on AmazonPrevents carb gumming during seasonal storage.
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