So this just happened to me and reading through these some of it makes sense.
Got in touch with a tech- he said most machine will have a diagnostic cheat-sheet in the compartment under the unit- you have to take the foot plate off to find it ( convenient, right? ) there's a list of error codes with the last (most recent) first.
They confirmed the press any button but the start/on-off buttons rapidly hit them 123-123-123.
He said to close the door and wait. For units with top mounted controls, watch the indicator light. It'll start flashing for the first diagnostic, pause with 1 flash, then flash again (does this twice.) Then do a second set of flashes. Once it does each set twice, it'll run a short cycle. Once complete it should show the error codes.
If the cheat-sheet is where he said, you can find it on the list and go from there with how to approach the resolution.