Sounds like a bad part of the power washer.
Gfci replacement plug power washer.
So with a 2 wire gfci plug and the washer sitting on dry ground it still tripped.
Works with all residential models.
It should be about 3 1 8 x 2 1 5.
Actual product may appear differently than in the photo with updates and upgrades but will still work with all residential models.
If i were you i would replace the cord with a 3 wire and just plug it in the garage gfci receptacle.
So the gfci was in fact part of the power washer and was getting hot but when replaced with a non gfci plug and plugged into a gfci receptacle everything went along fine.
Tower manufacturing shock buster 15 amp 125 volt general duty 3 wire grounding straight plug.
4 8 out of 5 stars 1 858.
Ar blue clean gfci replacement plug pw4221160 for electric pressure washers this also replaces part pw3084330 on older machines.
For pricing and availability.