I have stayed in many airbnb's in Madrid but this one was my favourite so far.
There's two major things - you're on the 3rd floor & there's no lift. Make peace with it but one thing which needs to be sorted is the temperamental heating.
The girl who checked me in couldn't help, the host had to contact the owner (in Switzerland) who contacted on the phone but wasn't too sure (but a nice guy). Even after the solution was found, it still continued to get error messages every day. It was really irritating.
Other than that, ALL amenities were flawless, so I'm giving it a 5 star despite the heating and stairs. Seriously guys - get the heating sorted and keep up the good work.