Based on our findings today, it might be time to think about getting a brand new system. Today we came out for main level furnace not heating trane 2011 natural gas 60k with matching 2.5 ton ac. Checked operations found failed digital thermostat. Performed safety inspection on furnace checked heat exchanger with digital camera found crack @ 7 o clock. Tagged furnace unsafe to operate in heating mode due to potential carbon monoxide fumes. Flue piping is not up to current code and client has minimal flood protection. Scheduled install supervisor for tomorrow last call to give options on updating as equipment is at full life expectancy