The water pump inside a pressure washer can lock up and sustain damage if the unit is exposed to sub-freezing temperatures. Water expands as it freezes, causing surrounding parts in a pressure washer to warp, bend or distort. For example, you may find that the line to the pressure washer spray nozzle is split, cracked, or shows other signs of damage. The internal pump typically makes a distinctive sound and behaves in predictable, if undesirable, ways when damaged by freezing.
Place the pressure washer in a garage or other location where it can thaw and the water inside can return to a liquid state.
Turn on the power to the washer, starting the equipment as you normally would.
Listen for an unusual humming or clanking sound. The pressure washer will typically shut down after a moment if the pump is damaged from freezing. If you use an electric pressure washer, the unit may also trip the circuit breaker or blow a fuse.
Shut off the unit if you hear any odd sounds, if it doesn't cut off automatically. Don't attempt to operate the pressure washer until it's serviced.
Pressure washer manufacturers typically exclude freeze damage from warranty coverage. Check with the manufacturer of your particular model for warranty details.