Ford and screen fitters say the elements fail which fail one half of the screen. Nope, the heating elements are in parallel not series, so one failing wont fail a side of the screen. Instead your windscreen wiper mechanism is fouling the delicate fol strip that supplies power to the screen. Ford wont admit this design fault unless more people complain to ford, they should be recalled. Mine is a ford focus titanium 06 model.
Below is my youtube video showing the reason my drivers side of the screen has faile, it funny from what ive read its always everyones drivers heater that fails!