When your pressure washer starts strong but repeatedly loses pressure during use, you’re dealing with one of the most frustrating issues that can happen during a cleaning project. This cycling between normal pressure and weak flow typically points to a few specific problems that are fortunately fixable with the right approach.
Step-by-Step Fixes
Step 1: Check Your Water Supply First
Start with the simplest solution. Turn off your pressure washer and disconnect the garden hose from the unit. Turn on your outdoor faucet fully and time how long it takes to fill a 5-gallon bucket. If it takes more than 50 seconds, your water supply is too weak. Most pressure washers need at least 2.5 gallons per minute to function properly.
Move to a different faucet if possible, or check if someone else is using water in your home. Sometimes the issue is as simple as a partially closed valve or a kinked garden hose that’s restricting flow.
Step 2: Clean or Replace the Inlet Filter
Locate the water inlet where your garden hose connects to the pressure washer. Inside this connection, you’ll find a small mesh filter that often gets clogged with sediment or mineral deposits. Unscrew the hose coupling and carefully remove the filter with needle-nose pliers.
Rinse the filter under running water, using an old toothbrush to remove stubborn debris. If the mesh is torn or heavily corroded, replace it immediately. These filters cost less than $10 and are available at most hardware stores. A clogged inlet filter is ideal for causing the exact pressure cycling you’re experiencing.
Step 3: Inspect and Clean the Spray Nozzle
Remove the spray tip from your wand and hold it up to the light. You should see a clear, round opening. If it looks partially blocked, soak the nozzle in white vinegar for 30 minutes to dissolve mineral buildup. Use a nozzle cleaning tool or a straightened paperclip to carefully clear any debris.
Never use metal objects that could enlarge the orifice. A damaged nozzle opening will permanently reduce pressure. If cleaning doesn’t help, try a different nozzle to see if the problem persists.
Step 4: Check for Air in the System
Air trapped in your pump causes pressure to build and release repeatedly. With the pressure washer off, squeeze the trigger on your spray gun and hold it for 30 seconds to release any trapped air. Connect your water supply and turn it on fully, then squeeze the trigger again until you see a steady stream of water with no sputtering.
Start your pressure washer while holding the trigger down. This prevents air pockets from forming during startup. If you still experience pressure loss, you might have a more serious air leak.
Step 5: Examine the Unloader Valve
The unloader valve regulates pressure when you release the trigger. A sticking or damaged unloader valve creates the exact symptoms you’re experiencing. While the engine is off, pull the recoil starter slowly and feel for unusual resistance or grinding sensations.
Some models allow unloader valve adjustment with a knob or screw near the pump head. Consult your manual for the correct procedure, as improper adjustment can damage your pump. This repair is best used in situations where other solutions have failed.
Likely Causes
Cause #1: Water Starvation
Your pressure washer pump needs consistent water flow to maintain pressure. When the water supply can’t keep up with demand, the pump alternates between building pressure and running dry. Check for undersized garden hoses (use 3/4 inch diameter, not 5/8 inch), excessive hose length (keep it under 50 feet), or low water pressure from your home’s system.
Test by running water directly from your faucet into a bucket while the pressure washer operates. If flow reduces dramatically when the washer runs, you’ve found your problem. The solution is upgrading your hose, moving closer to the water source, or using the unit during off-peak water usage times.
Cause #2: Worn Pump Seals
Pressure washer pumps use special seals to maintain high pressure. When these seals wear out, typically after 300-500 hours of use, they allow water to bypass internally. You’ll notice the pressure drops more frequently as the pump heats up during use.
Look for water dripping from the bottom of the pump or oil that appears milky (indicating water contamination). Pump seal replacement is not recommended when you’re mid-project, as it requires disassembly and special tools. This issue is ideal for professional repair.
Cause #3: Thermal Relief Valve Cycling
Modern pressure washers include a thermal relief valve that opens when water temperature exceeds safe limits. If you run your washer in bypass mode (trigger released) for more than 2-3 minutes, hot water dumps out and cold water enters, causing pressure fluctuations.
Always squeeze the trigger at least every 30 seconds when the engine is running. If your model has a thermal relief valve (a small brass fitting on the pump), check if it’s leaking constantly, which indicates failure and needs replacement.
When to Call Expert Help
Contact a pressure washer repair technician when you notice oil leaking from the pump, unusual knocking sounds during operation, or if the pressure problem persists after trying all basic troubleshooting steps. Professional diagnosis makes sense when your unit is under warranty or worth more than $500.
Most repair shops charge $50-100 for diagnosis in 2025, which they often waive if you proceed with repairs. Pump rebuilds typically cost $150-300, while complete pump replacement runs $200-500 depending on your model.
Copy-Paste Prompt for AI Help
“My [brand and model] pressure washer starts with normal pressure but loses it repeatedly during use. I’ve checked the water supply (it fills a 5-gallon bucket in X seconds), cleaned the inlet filter and spray nozzle, and bled air from the system. The pressure drops every X seconds and returns after X seconds. The unit is X years old with approximately X hours of use. What specific troubleshooting steps should I try next for this model?”