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 Upland, 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.
Warning Signs for Furnace Repair
The sooner you notice these red flags, the easier and cheaper the fix. Watch for these telltale signs:
- Squeals, scrapes, or grinding noises behind the blower door
- The igniter glows and clicks, yet no flame ever appears
- Soot, rust, or moisture near the furnace cabinet or vent pipe
- A fan that keeps running while the registers blow cool air
- Frequent on-off cycling that never reaches the thermostat setting
- Loud booms at startup caused by delayed ignition
- A flame that burns soft and yellow rather than steady blue
- Burners light, run a few seconds, then shut down repeatedly
Early Action Saves Money
Most HVAC failures start small, a weak capacitor, a squealing blower, a system that runs a little longer each week. Don't wait, call (909) 310-3067 and we'll take a look right away.
