Pressure washers & generators

Pressure washer loses prime / has to be restarted repeatedly

A pump that loses prime repeatedly usually has a small air leak on the suction side, an intermittent water supply, or a worn check valve letting the pump run dry between uses.

Difficulty
Moderate
Time
15–30 minutes
DIY cost
$5–$25
Pro cost
$80–$180

Symptoms

  • Pressure drops to nothing partway through use
  • Have to disconnect and reconnect the hose to restore pressure
  • Works fine at first then gradually loses pressure
  • Priming issue returns even after purging air

Likely causes

  • CommonSmall air leak at the inlet fitting or hoseAir drawn in on the suction side prevents the pump from maintaining prime.
  • CommonInconsistent water supply pressure or flowA weak spigot, long garden hose run, or shared water use elsewhere in the house can starve the pump intermittently.
  • PossibleWorn inlet check valveThis valve should prevent backflow and air ingress; wear lets air sneak in between pump strokes.
  • PossibleDebris partially blocking the inlet filterA partial clog can be enough to starve the pump under sustained use even if flow looks fine briefly.

What to do

  1. Check the inlet fitting where the garden hose connects for a tight, leak-free seal, and inspect the O-ring there.
  2. Confirm the garden hose is fully open at the spigot and not shared with another water use during your job.
  3. Clean the inlet filter screen thoroughly, since a partial clog can cause exactly this intermittent starving pattern.
  4. Shorten the garden hose if it's an especially long run, since long thin hoses restrict supply flow.
  5. Purge air fully at startup by running with the trigger open for 15–20 seconds before use.
  6. If priming issues return mid-job even with good supply, the inlet check valve inside the pump likely needs replacement.
  7. A repair shop can pressure-test the suction side to pinpoint a small air leak that's hard to find by inspection alone.

Tools and parts

  • None required for basic checks
Pressure washer inlet filter screenSearch: “pressure washer inlet filter screen”
Pump check valve kitSearch: “pressure washer pump check valve kit”

When to call a pro

If the pump keeps losing prime despite good water supply and a clean filter, a repair shop can find a suction-side leak or replace a worn check valve.

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.