Pressure washers & generators

Pressure washer runs but won't build any pressure

If water flows but there's no pressure at all, air is usually trapped in the pump, or the unloader valve is stuck in bypass mode letting all the water flow back around instead of out the nozzle.

Difficulty
Moderate
Time
15–45 minutes
DIY cost
$15–$40
Pro cost
$90–$200

Symptoms

  • Water flows out like a garden hose with no force
  • No change in pressure with different nozzle tips
  • Machine runs normally otherwise
  • Started fine before but now has zero pressure

Likely causes

  • CommonAir locked in the pumpIf the pump ran dry even briefly, it can lose prime and need to be purged of air.
  • CommonUnloader valve stuck openThis valve diverts water when the trigger is released; if stuck, it can dump all pressure even with the trigger pulled.
  • PossibleWrong nozzle tip installedA very wide-angle or soap nozzle produces little to no pressure by design.
  • PossibleTorn or worn pump seals/O-ringsWater bypasses internally instead of pressurizing, often after age or a period of dry running.
  • Less commonCracked or disconnected internal hoseA hidden hose or fitting inside the housing may have failed.

What to do

  1. Make sure a high-pressure (not soap) nozzle tip is installed; check for a low-pressure detergent setting that may be engaged.
  2. Turn off the machine, disconnect the high-pressure hose from the gun, and run water through briefly to purge trapped air from the pump.
  3. Reconnect everything and run with the trigger squeezed for 15–20 seconds to let the pump re-prime.
  4. Confirm the water supply is fully on and unrestricted at the inlet.
  5. Inspect the trigger gun and wand connections for a loose fitting that could be venting pressure.
  6. If pressure still doesn't build, the unloader valve may be stuck; consult the owner's manual for its location and adjustment screw.
  7. If none of this restores pressure, internal pump seals have likely failed and need professional repair or pump replacement.

Tools and parts

  • None required for basic checks
Pump seal/O-ring kitSearch: “pressure washer pump seal repair kit”
Unloader valveSearch: “pressure washer unloader valve replacement”

When to call a pro

If purging air and checking the nozzle doesn't restore pressure, a repair shop can test and replace the unloader valve or pump seals.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.