Diagnosis
The quick-connect coupler on the pump outlet is damaged or the hose fitting's collets are worn. Dirt in the mechanism is also common.
How to Fix It
Disconnect power and release all pressure. Inspect the female coupler on the machine. Look for broken or bent retaining balls inside. Clean the coupler and the male hose end with a brush, then apply a drop of light oil to the collets.
If That Didn't Work
The spring inside the coupler may have lost tension. The entire pump outlet coupler assembly needs replacement. It threads directly into the pump head.
Heads Up
Always depressurize the system before disconnecting the hose. Trying to force a connection under pressure will destroy the coupler and is extremely dangerous.