rear window screen not heating up. could there be a brake in cable

I took my car into the dealer for a service whilst it was still under waranty. A couple of weeks later there was some wet weather and I switched on the rear screen heater... which didn't, as such, actually work! I checked the fuse box.. The rear screen heater fuse was blown. Strange, that. I've never, ever, had one blow before! You've not had your car in for a dealer service recently, have you?