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 Santa Rosa, CA, 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. These are the signals our technicians see most often:
- Short cycling every few minutes without reaching the setpoint
- Water, rust stains, or black soot around the flue or cabinet
- Squeals, scrapes, or grinding noises behind the blower door
- Burners light, run a few seconds, then shut down repeatedly
- Loud booms at startup caused by delayed ignition
- The blower runs constantly but the air never warms
- The furnace clicks and glows but the burners never light
- A pilot or burner flame that is lazy yellow instead of crisp blue
Don't Wait for a Total Failure
A failing capacitor, clogged condensate drain, or dirty flame sensor rarely fixes itself and usually gets more expensive to address the longer it runs. If you notice any of these signs, call (707) 210-0204 for a prompt inspection.
