Hi bossko,
I cant remember which fuse it is, I checked them all and they were all fine, but there are plenty of info online for this. I thought I would mention that after repairing my airbag fault,( another saga), the demister stopped working altogether. What I did to fix it was remove the plastic cover under the bonnet in front of the driver seat. I removed the fan and comnnections which was quite simple. The drain hole was blocked so I cleaned this out and then noticed that some connectoers on the resistor were dirty, prob due to water sitting there. I cleaned the connectors up, bottom 2 on the resistor and sprayed with WD40. Put everything back together and everything works fine.
Hope this helps
jackenrye