From the hallway, a furnace that will not heat looks the same no matter what broke. Inside the cabinet, though, everything happens in a strict order: 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 Oakland 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.
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. These are the signals our technicians see most often:
- Clicking and a glowing igniter with no burner flame
- Short cycling every few minutes without reaching the setpoint
- Repeated shutdowns just seconds after the burners light
- Air moving through the vents that never gets warm
- Yellow, wavering burner flames where they should be sharp blue
- Squeals, scrapes, or grinding noises behind the blower door
- Rust streaks, soot, or water around the cabinet or flue
- Booming or banging at light-off from delayed ignition
Act Before It Gets Worse
A failing capacitor, clogged condensate drain, or dirty flame sensor rarely fixes itself and usually gets more expensive to address the longer it runs. Call (510) 201-4731 at the first sign of trouble.
