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 Kent, WA, 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.
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:
- The blower runs constantly but the air never warms
- Rust streaks, soot, or water around the cabinet or flue
- The igniter glows and clicks, yet no flame ever appears
- A bang or boom when the burners ignite late
- Squealing or grinding from the blower compartment
- A furnace that shuts off every few minutes before the house warms up
- Repeated shutdowns just seconds after the burners light
- A flame that burns soft and yellow rather than steady blue
Early Action Saves Money
A failing capacitor, clogged condensate drain, or dirty flame sensor rarely fixes itself and usually gets more expensive to address the longer it runs. Call (253) 660-4929 at the first sign of trouble.
