Mini Roadster mirror heater issue

That's a rather peculiar issue. I experienced something vaguely similar with my Roadster; the rearview mirror heater on mine was acting up erratically. Have you checked the fuses related to the mirror heating circuit? It might also be worthwhile to inspect the wiring harness where it enters the door, as those areas are prone to damage. Does the error memory give any specific codes?

Good call about the wiring harness. Where exactly is that located? And did your issue throw an error code too?

Yes, it did throw a code, though I don't recall the specifics. I'd start by inspecting the harness where it passes from the A-pillar to the door. Give the wires a wiggle, see if anything changes. If you're not comfortable doing that, I would recommend taking it to a workshop. It does sound like an electrical fault, and those can be tricky to diagnose without the right tools and experience. The heater element is important and a faulty car electronics system can be dangerous.

Took it to the shop as you suggested. Turns out it was a corroded connector on the driver's side mirror. They cleaned it up and now the heater element works perfectly. Thanks for the advice!