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 Kirkland, WA, 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.
For air conditioning breakdowns, see AC Repair.
Warning Signs for Furnace Repair
The sooner you notice these red flags, the easier and cheaper the fix. Keep an eye out for the following clues:
- The furnace clicks and glows but the burners never light
- Water, rust stains, or black soot around the flue or cabinet
- A flame that burns soft and yellow rather than steady blue
- A fan that keeps running while the registers blow cool air
- Grinding or high-pitched squeals from the blower
- Frequent on-off cycling that never reaches the thermostat setting
- Loud booms at startup caused by delayed ignition
- Repeated shutdowns just seconds after the burners light
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. Call (425) 969-3519 at the first sign of trouble.
