Diagnosis
Some warmth is normal, but a strong hot plastic smell and excessive heat usually mean the pump is running dry or with insufficient water flow, causing friction and overheating.
How to Fix It
Immediately shut it off and let it cool. The number one cause is a restricted water inlet. Go back to your water source. 1) Ensure the garden hose isn't kinked anywhere. 2) Check that the faucet is all the way on. 3) Unscrew the inlet filter on the washer (where the hose connects) and rinse it clean. A partially blocked filter is a frequent culprit for reduced flow that leads to overheating. Once everything is clear, restart with the trigger pulled.
If That Didn't Work
You might be using too long or too narrow of a garden hose. For this model, don't use a hose longer than 50 feet, and make sure it's a standard 5/8" diameter. A long, skinny hose can't deliver enough gallons per minute (GPM) to keep the pump cool.
Heads Up
That smell is a warning. Continuously running it hot will warp internal pump components and melt plastic parts. The machine has a thermal shut-off, but it's a last resort. If you catch the smell, stop and find the cause. Always provide the pump with a strong, cool feed of water—that's its lifeline.