Los Angeles furnaces sit idle most of the year and are then expected to work on the first cold night. Some problems are a two-minute fix; others need a technician. Here is how to tell — safely.
Safety first
If you smell gas, don't touch switches or try to relight anything. Leave the house and call SoCalGas or 911 from outside. If a carbon monoxide alarm goes off, get everyone out and call 911.
Six checks you can do
- The thermostat is set to Heat and above the room temperature; replace the batteries if the screen is blank.
- The furnace switch — it looks like a light switch near the unit — is on, and the breaker hasn't tripped.
- The front panel is closed properly; most furnaces won't run while the door safety switch is open.
- The filter isn't clogged; a blocked filter can make the furnace overheat and shut itself off.
- Gas is on: other gas appliances work, and the valve on the furnace's gas line is open (handle in line with the pipe).
- The status light: many furnaces blink an error code through a small window, with the code chart inside the panel. Write the pattern down.
What the symptoms usually mean
- Clicks, then nothing — usually an ignition problem: the igniter or the ignition control.
- Lights for a few seconds, then shuts off — often a dirty flame sensor.
- Runs but blows cold air — the burners aren't staying lit, or the thermostat is set to fan only.
- A high-efficiency furnace with plastic vent pipes won't start — check for a blocked condensate drain.
- A burning-dust smell on the first cold night that fades within the hour is normal. A smell that stays, or any smell of gas, is not.
When to call
If the checks don't fix it, if the furnace keeps shutting off, or if the error code points to the igniter, flame sensor, pressure switch or control board, book a visit. The $69 service call covers the diagnosis and is applied to the repair; you get the price before any work, and repairs carry a 90-day warranty.
Before the cold nights
A fall tune-up — cleaned flame sensor, checked igniter and safety switches, a new filter — catches most first-cold-night failures before they happen.