The answer is "not much".

You rented the house knowing it was a metal front door. It's not as if it is a repair due to it being broken, or a maintenance issue like the gutters. You just don't like that it gets hot. But you knew it was metal when you rented the house so the landlord is under no obligation to fix it.

Says she who also rents , and has had over 10 tradies through the house in the last few weeks to fix maintenance issues or broken things