I will answer my own question.
This video covers several causes of 100016 error.
when I got back to the printer I found a loose ribbon cable (base to scanner, one of three cables)
Only needed to remove two screws.
colinK
This is not my printer.
To the best of my knowledge printing, scanning or copying was working until user left it too long without use and print heads needed cleaning.
I carefully cleaned print heads manually as described in a YouTube video.
After refitting the printer head and the white boxes...