Homeowner Guide
A furnace that lights briefly and shuts back down is trying to tell you something. The useful details are the startup pattern, how long the flame stays on, whether the blower runs, and whether any safety warning shows up.
The thermostat calls for heat, the inducer or blower may start, burners may light, then the flame shuts off before the furnace has a normal heating run. Some systems retry several times and then stop until the next call for heat or reset.
A furnace that will not stay lit can involve ignition, flame sensing, airflow, pressure switch, venting, gas supply, control, or safety-limit behavior. The $95 Springfield Diagnostic helps separate the symptom from the repair before parts are quoted. Nearby towns may cost more.
Read the diagnostic pageYou can check thermostat mode and the filter, but do not open furnace panels or keep forcing restarts. If you smell gas, leave the area and contact the gas utility or emergency services from a safe location. If you see smoke, flame rollout, arcing, a hot electrical smell, or another breaker trip, shut the system off and stop testing.
