furnace leaks gas, landlord problems

my furnace leaks gas, gas company red tagged it,landlord says i need to light it if i want heat,what should i do?

If it leaks, the landlord is responsible for fixing it. Don't light it. It's dangerous.

I would also call the city building codes office--that has to also be a serious code violation.

Call code enforcement, the building inspector, the housing authority, and/or the health department and report this. Send a certified letter to the LL demanding repair on the furnace immediately. Keep a copy. If the LL fails to take action within a reasonable time (3-5 days at most), deposit future rents with the clerk of court (this is called rent withholding). The rent must be paid on time and in full to the clerk. They notify the LL that they have his rent so he can't evict you. He must make repairs in order to get his rent money. Lack of heat is a habitability issue and qualifies you for rent withholding.