LEASE with option to purchase Maintenance?

If there is anyone with some knowledgable advice, please let me know, on lease with option to purchase who is responsible for fixing or replacing a 30 year old furnace, that had not been maintained since i got here, and now its stopped working. my contract says to keep the property in the same condition or as good condition as it was when we moved in. I have had it maintenanced 2 times in one year, i was going to switch propane companies they wouldnt do it, because the heat exchanger was leaking carbon bonoxide poisening, Then the darned thing quit on us. Lease with option to purchase also includes moving out if something is not livable. anyway, everything is falling apart, I dont think i have to continue to be gullable because i need a place for my kids to live. To fix something up that was never kept together and that is 30 years old. Give me some good advice, they are wanting me to pay back, for the price of 2,000.00 on a heater. That went out cause of age. I have proof .