First Answer from Mark, December 2008 worked a treat, thanks.
As he said, you need the "C" key and on my machine, there is one unmarked position past PGM, expect that is MC.
Original message:
Hi.
Turn the key to MC position (only your key marked 'C' will turn to here).
Turn power off at wall.
Hold the clear button down (C)
Turn power on at wall.
It should print '.....CS' on the paper.
Remember, this will CLEAR ALL DATA AND PROGRAMMING, so only do it if you have tried everything else.
Mark
Jim-4401, April 2017