Thanks, I had found this in a previous thread last week and tried it with no success. The following looked promising but the F / C is a switch and not a button...

FACTORY DEFAULTS - If, for any reason it is desirable to
return all stored settings back to the factory default
settings, press the Fan button. While holding the Fan
button in, press the Down button for 2 sec. All icons will
appear. Press and hold in the F / C button until Fd
appears. This resets all factory settings, except for the
equipment type.