Why is the LCD screen on my Optima 701 blank? (And how do I fix it?)?

Since I moved into this flat, the screen on the CH boiler has been blank, like there's no power getting to it.

The days (and mornings!) are getting colder now, so I'd like to be able to have the flat a little warmer for me getting up, but without the screen working, there's no timer functionality. I just have to use the knob to turn the CH on manually.

The CH system works fine, hot water and radiators, it's just the timer that doesn't work.

Is there a backup battery that's died, or a fuse or something?

Thanks in advance for any help, folks! :)