Diagnosis
Surging is almost always caused by air getting into the water supply. The pump is trying to pressurize a mix of water and air. The usual entry point is a loose or poorly sealed connection on the inlet side.
How to Fix It
Start at the tap. Make sure the garden hose is screwed on tightly. Then, check the connection where the hose attaches to the pressure washer's inlet. Ensure the black plastic connector is hand-tight plus a quarter-turn with pliers (don't over-tighten and crack it). Also, check that the rubber washer inside the garden hose connector is present and not damaged.
If That Didn't Work
If connections are tight, the source might be a pin-hole leak or crack in the garden hose itself, which can suck in air when under pressure. Try a different hose. A less common cause is a failing inlet valve inside the pump, which would require a pump service.
Heads Up
This surging puts extra stress on the pump and hose connections. Fixing an air leak isn't just about performance—it prevents premature wear and potential blowouts at the fittings.