Already done Sebastian, thanks.

Thanks Sebastian, I can see the clock can be adjusted. At the moment, with the old battery still installed (I did measure it and it seemed ok to me @4.2V but will accept it may be borderline) I can adjust the time but that is all, the temperatures from the thermistors are not there, this is why I believe it may need initialising. I can also enter the options pages where you can set various options like room thermostat fitted or not and hot water cylinder temperature 60 or 70 degrees and I believe there will be a 'secret' code in there somewhere to initialise the control board. It isn't in the manual, at least, not the manual for mere users, it will be a reserved engineering code.

I am in this boat. Replacing the battery is not a problem. The problem is what is the procedure to reinitialise the control unit afterwards? What values need to be put back and what button presses achieve that?