2) Faulty switch: The switch that turns on the rear window demister may be faulty. Try wiggling the switch or applying some contact cleaner to see if this restores functionality.
3) Broken wire: The wire that supplies power to the rear window demister may be broken or damaged. Check the wiring for any breaks or damage and repair as necessary.
4) Faulty relay: The rear window demister may be controlled by a relay, which may have failed. Check the relay (usually located in the fuse box) and replace it if necessary.
5) Faulty defroster grid: The defroster grid on the rear window may be damaged or have a poor electrical connection. Check the grid for any breaks or damage and repair as necessary.