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 Arcadia, 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.
When the AC quits in summer, see AC Repair.
Warning Signs for Furnace Repair
The sooner you notice these red flags, the easier and cheaper the fix. Here are the most common indicators that it's time to call a professional:
- Squeals, scrapes, or grinding noises behind the blower door
- 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
- Flames that start, last a few seconds, and go out again and again
- The blower runs constantly but the air never warms
- A furnace that shuts off every few minutes before the house warms up
- Loud booms at startup caused by delayed ignition
Act Before It Gets Worse
What seems like a minor issue today can take out a compressor or heat exchanger tomorrow. Don't wait, call (626) 231-7816 and we'll take a look right away.
