A modern furnace runs a strict startup sequence, and knowing where the sequence breaks is most of the diagnosis. The thermostat calls, the inducer motor spins up to prove draft through a pressure switch, the hot surface igniter glows, the gas valve opens, the burners light, the flame sensor confirms fire, and only then does the blower deliver heat to the house. In Franklin, TN, the failures cluster at predictable points: a flame sensor coated in oxide that can no longer prove the flame, a hot surface igniter cracked from years of thermal cycling, a pressure switch that will not close because the inducer is weak or the condensate trap on a high-efficiency model has clogged, or a control board with a burned relay. Each one stops the sequence cold, and each one mimics the others from the hallway.
For air conditioning breakdowns, see AC Repair.
Warning Signs for Furnace Repair
Catching these issues early helps you avoid costly problems. Watch for these telltale signs:
- The blower runs constantly but the air never warms
- Burners light, run a few seconds, then shut down repeatedly
- A flame that burns soft and yellow rather than steady blue
- Loud booms at startup caused by delayed ignition
- Water, rust stains, or black soot around the flue or cabinet
- Frequent on-off cycling that never reaches the thermostat setting
- The igniter glows and clicks, yet no flame ever appears
- Squeals, scrapes, or grinding noises behind the blower door
Don't Wait for a Total Failure
Left unchecked, even a small fault or temperature swing often signals a system working its way toward a breakdown. At the first hint of a problem, call (615) 537-0369 for a fast inspection.
