Grounds for breaking rental lease early, lack of maintenance by landlord?

I leased an efficiency apt. from someone I know. Before I moved in I thouroughly cleaned it, which had not been done in some time, put new carpeting in it, painted it and bought a new stove and fridge. About a month ago, the old wall heater started putting out soot all over the walls and cabinets, and then the place filled up from carbon monoxide due to lack of maintenance with the heater. The landlord did get that fixed, but refused to pay for the soot damage cleanup which ended up costing over $200. I have had one problem after another, with an old toilet overflowing several times, etc. I would just like to walk away, not expecting my deposit back. The stove and fridge and improvements I am also willing to walk away from, just to get a place I feel safe in. Does anyone know what kind of maintenance a landlord is obligated to do? Is there any grounds getting out of the lease?