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 San Marcos, TX, 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.
Signs You Need Furnace Repair in San Marcos
Catching these issues early helps you avoid costly problems. Watch for these telltale signs:
- Grinding or high-pitched squeals from the blower
- A bang or boom when the burners ignite late
- Short cycling every few minutes without reaching the setpoint
- Air moving through the vents that never gets warm
- Clicking and a glowing igniter with no burner flame
- Rust streaks, soot, or water around the cabinet or flue
- A flame that burns soft and yellow rather than steady blue
- Repeated shutdowns just seconds after the burners light
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. Don't wait, call (737) 344-9567 and we'll take a look right away.
