Constructive Eviction and the Implied Warranty of Habitability

Steve is renting a property from Billy. One evening Steve tripped and fell down the stairs. The issue is that one of the stairs in the common area was faulty. Billy knew about the stair, but he had never got around to fixing it.

Steve injured his leg, so he decided to return to his room. The heater was not working (and it was in the middle of winter). Steve had told Billy about the faulty heater for months, but Billy never got around to fixing it. There is a local ordinance that requires landlords to repair heaters. Additionally, assume that this jurisdiction includes the implied warranty of habitability. The jurisdiction recognizes constructive eviction, and it follows the majority rule of when landlords are liable for injuries.

What causes of action does Steve have?

What remedies does he have for the faulty heater?