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 moving heat through the ducts. Most of the diagnosis comes down to finding the broken link. In Daly City 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.
Warning Signs for Furnace Repair
Catching these issues early helps you avoid costly problems. Here are the most common indicators that it's time to call a professional:
- The igniter glows and clicks, yet no flame ever appears
- A pilot or burner flame that is lazy yellow instead of crisp blue
- Water, rust stains, or black soot around the flue or cabinet
- A furnace that shuts off every few minutes before the house warms up
- Loud booms at startup caused by delayed ignition
- A fan that keeps running while the registers blow cool air
- Repeated shutdowns just seconds after the burners light
- Grinding or high-pitched squeals from the blower
Don't Wait for a Total Failure
A failing capacitor, clogged condensate drain, or dirty flame sensor rarely fixes itself and usually gets more expensive to address the longer it runs. At the first hint of a problem, call (650) 220-0819 for a fast inspection.
