This post overlaps with a fuller one: Heater Not Turning On? Eight Checks Before You Call.
Most no-heat calls on the first cold night in Pasadena, CA come down to the thermostat, a switch or breaker, a packed filter, or a furnace that has locked itself out. That is the short version of our full heating guide.
Know what you have
The 1900s to 1930s bungalows around Pasadena and Altadena often have a wall or floor furnace with no ducts, some still on a standing pilot. Post-war ranch homes usually have a gas furnace in a closet, garage or attic. Newer homes may run a heat pump, the air conditioner in reverse.
The safe checks
- Thermostat. Heat, not Cool or Off, setpoint a few degrees above the room, fresh batteries if the screen is dim. Then wait five minutes for the startup sequence.
- The switch and the breaker. A switch beside the furnace looks like a light switch; people flip it by accident. Check the breaker box too; reset a tripped breaker once.
- The blower door. It has a safety switch. Left loose after a filter change, nothing runs.
- The filter. Packed, it starves the furnace of airflow and the limit switch trips.
- Registers and returns. Supply registers open, nothing over the return grille.
- One power cycle. Off, thirty seconds, on. That clears a lockout once, not twice.
What each symptom points to
- Nothing at all: thermostat, switch, breaker or blower door.
- Clicks but no flame: the ignitor, a pressure switch, or a gas valve not opening.
- Lights, runs a few seconds, goes out: a dirty flame sensor.
- Runs but the house stays cold: the filter, leaking attic ducts, or a furnace never big enough.
- Shuts off and comes back on its own: overheating on the limit switch, almost always airflow.
Stop and call if you smell gas (leave first, call the gas company from outside), if the furnace locks out after a reset, a breaker trips twice, a carbon monoxide alarm sounds, or water pools at the furnace. That is furnace repair and wall and floor furnace repair work.
The full guide: Heater Not Turning On? Eight Checks Before You Call.
Our diagnostic is $69, quoted before we book and credited toward the work. Call Boost Services, 818-277-5056, 6am to 10pm, seven days a week, or book online.
Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.