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 Oshkosh, WI, 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.
When the AC quits in summer, see AC Repair.
Warning Signs for Furnace Repair
Spotting the early warning signs lets you act before the problem gets expensive. These are the signals our technicians see most often:
- A fan that keeps running while the registers blow cool air
- Repeated shutdowns just seconds after the burners light
- The igniter glows and clicks, yet no flame ever appears
- A bang or boom when the burners ignite late
- A flame that burns soft and yellow rather than steady blue
- Short cycling every few minutes without reaching the setpoint
- Squeals, scrapes, or grinding noises behind the blower door
- Rust streaks, soot, or water around the cabinet or flue
Act Before It Gets Worse
Most HVAC failures start small, a weak capacitor, a squealing blower, a system that runs a little longer each week. At the first hint of a problem, call (920) 516-9323 for a fast inspection.
