From the hallway, a furnace that will not heat looks the same no matter what broke. Inside the cabinet, though, the sequence is strict: inducer on, pressure switch closed, igniter glowing, gas valve open, burners lit, flame proven, and finally the blower sending heat through the house. Diagnosis is mostly a matter of finding where that chain breaks. In San Francisco homes, it tends to be the same handful of culprits: a flame sensor coated in oxide, a hot surface igniter cracked by thermal cycling, a pressure switch held open by a tired inducer or a plugged condensate trap, or a control board with a burned relay.
For air conditioning breakdowns, see AC Repair.
Signs You Need Furnace Repair in San Francisco
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:
- Water, rust stains, or black soot around the flue or cabinet
- Burners light, run a few seconds, then shut down repeatedly
- The furnace clicks and glows but the burners never light
- Air moving through the vents that never gets warm
- A furnace that shuts off every few minutes before the house warms up
- Loud booms at startup caused by delayed ignition
- Grinding or high-pitched squeals from the blower
- A pilot or burner flame that is lazy yellow instead of crisp blue
Don't Wait for a Total Failure
Most HVAC failures start small, a weak capacitor, a squealing blower, a system that runs a little longer each week. If you notice any of these signs, call (415) 234-5360 for a prompt inspection.
