Symptoms
- Spray surges between strong and weak
- Machine seems to cycle on and off under pressure
- Vibration or knocking felt through the wand
- Pressure was steady before and started pulsing recently
Likely causes
- CommonAir in the pump or hoseTrapped air causes uneven flow until it's purged.
- CommonClogged water inlet filterA dirty screen restricts and varies water flow to the pump.
- PossibleWorn unloader valveThis valve can stick or wear, causing pressure to cycle unevenly.
- PossibleInsufficient water supplyLow incoming water flow causes the pump to cavitate.
- PossibleWorn pump seals or valvesInternal wear in the pump can cause inconsistent pressure over time.
What to do
- Shut off the machine and check the water inlet filter screen for debris, cleaning it if dirty.
- Make sure the garden hose supplying water is fully open and not too long or thin.
- Purge trapped air by running the unit without the nozzle attached until flow is steady.
- Inspect all hose connections for leaks that could let air in.
- Test with a different, clean nozzle tip to rule out a clog.
- Let the pump run briefly on a garden hose bib to see if pulsing continues without the spray gun.
- If pulsing continues after these checks, the unloader valve or pump likely needs professional repair.
Tools and parts
- Garden hose
- Nozzle cleaning pin
Pressure washer inlet filterSearch: “pressure washer water inlet filter”
When to call a pro
A pressure washer repair shop can rebuild or replace the unloader valve or pump if basic troubleshooting doesn't fix the pulsing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.