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 Reston, VA, 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
Recognizing the warning signs early can save you time and money. Here are the most common indicators that it's time to call a professional:
- A pilot or burner flame that is lazy yellow instead of crisp blue
- Air moving through the vents that never gets warm
- Burners light, run a few seconds, then shut down repeatedly
- A furnace that shuts off every few minutes before the house warms up
- Water, rust stains, or black soot around the flue or cabinet
- Clicking and a glowing igniter with no burner flame
- A bang or boom when the burners ignite late
- Squeals, scrapes, or grinding noises behind the blower door
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. Don't wait, call (571) 741-3122 and we'll take a look right away.
