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 Mateo, CA, the failures cluster at predictable points: an oxide-coated flame sensor, 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.
When to Call for Furnace Repair in San Mateo
Catching these issues early helps you avoid costly problems. These are the signals our technicians see most often:
- Grinding or high-pitched squeals from the blower
- Frequent on-off cycling that never reaches the thermostat setting
- Soot, rust, or moisture near the furnace cabinet or vent pipe
- A bang or boom when the burners ignite late
- The blower runs constantly but the air never warms
- A pilot or burner flame that is lazy yellow instead of crisp blue
- The igniter glows and clicks, yet no flame ever appears
- Flames that start, last a few seconds, and go out again and again
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. At the first hint of a problem, call (650) 220-0817 for a fast inspection.
