I have a clothes washer which came with a gfci adapter. The cord didn't quite reach the nearest outlet, so we had the washer plugged into a (grounded) 3-outlet interior extension cord, then to the GFCI adapter, then to a normal outlet.
I recently had an electrician come out to install an outlet nearer to the washer. When we plug the washer directly into this new GFCI outlet, it trips sometime during the prewash cycle. When we plug the washer into its GFCI adapter, and then into the new GFCI outlet, the new outlet trips. When we plug the washer into the extension cord then directly into the new GFCI outlet, the outlet trips. I tried replacing the extension cord with a different one. I tried eliminating the extension cord (not a viable long term solution).
When I plug my heavy duty blender or vacuum cleaner into the new outlet and turn them on high, the outlet does not trip.
The result is always the same: old outlet + washer works, new outlet + washer trips, new outlet + something else works.
The electrician asserts there's nothing wrong with the outlet, that something must be wrong with the washer. It's clear to me that it's some combination. What could be causing this?