who rescued luis?

I was wondering the same thing. The only thing I can think of is that his mother got him out, since she heard him pounding in the vent when she was in the shower room. This would explain why she was so strict with him about peeping on the girls. Another possibility is that the maintenance man heard him when he eventually came back to the boiler room.

It's weird that the movie doesn't show how he got out; maybe the scene was shot, but ended up on the cutting room floor.