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 Somerville, MA, 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.
Cooling trouble instead? See AC Repair.
Warning Signs for Furnace Repair
Catching these issues early helps you avoid costly problems. Keep an eye out for the following clues:
- The igniter glows and clicks, yet no flame ever appears
- Grinding or high-pitched squeals from the blower
- Repeated shutdowns just seconds after the burners light
- Rust streaks, soot, or water around the cabinet or flue
- A pilot or burner flame that is lazy yellow instead of crisp blue
- Frequent on-off cycling that never reaches the thermostat setting
- Air moving through the vents that never gets warm
- A bang or boom when the burners ignite late
Act Before It Gets Worse
A failing capacitor, clogged condensate drain, or dirty flame sensor rarely fixes itself and usually gets more expensive to address the longer it runs. At the first hint of a problem, call (857) 767-3378 for a fast inspection.
