Performed heating maintenance on a Trane two stage 80% efficient natural gas furnace. Pulled and cleaned flame sensor Changed air filter Replaced humidifier water panel High fire gas pressure 3.5 Temp rise 43 degrees Low fire gas pressure 1.7 Temp rise 43 Blower is clean No carbon monoxide present in return or supply ducts or around the furnace. Opened humidifier bypass damper Set humidistat to 35% No water leaks from the humidifier at this time Furnace operating within factory specifications at this time. Replaced thermostat batteries