Homeguides.SFGate.com and eHow offer detailed troubleshooting guides specific to the Trane Xe80 residential gas furnace. BobVila.com hosts an in-depth guide to troubleshooting gas furnaces in general.
To troubleshoot a Trane Xe80, first make sure the thermostat is set to "heat," and select a temperature low enough for the unit to turn on. Check for blown fuses or tripped breaker switches, and repair or replace them if necessary. Ensure that the air filter and flue systems are clean and undamaged and that the register vents are open and unobstructed. If you smell gas, turn off the main gas valve, and alert your natural gas company.