Diagnosis
This is classic unloader valve behavior. The valve is cycling because it cannot stabilize the system pressure, often due to a worn nozzle or a trigger gun leak.
How to Fix It
Inspect your spray wand tip. A worn or damaged orifice causes low pressure and surging. Try a different, known-good tip. If surging stops, replace the worn tip.
If That Didn't Work
There may be a small leak in the trigger gun or high-pressure hose fittings. Even a tiny leak downstream of the pump causes the unloader to cycle constantly. Listen for hissing.
Heads Up
Never run the pressure washer for more than a few minutes with the trigger released. The constant bypass cycling overheats the pump oil rapidly.