The short answer
Most furnace calls in South Pasadena come from failed igniters, dirty flame sensors, pressure switch faults, blower problems or clogged filters. We read the furnace's error code, test the startup sequence, fix the cause and confirm the unit is venting safely.
In South Pasadena, the furnace usually spends spring through fall sitting quietly in a hall closet, attic or garage. Then the first cool evening arrives, someone turns the thermostat up, and months of settled dust, a weakened igniter or a forgotten filter all get tested at once. If the heat does not come on, or comes on and quits, our technicians can be there from Pasadena, three miles to the northeast. We repair standard and high-efficiency gas furnaces of all major brands throughout 91030, and every visit includes a safety check of the burners, venting and heat exchanger.
Start with the blinking light
Nearly every furnace built in the last few decades has a small window on the blower door where a status light blinks a pattern. A sticker inside the door explains what the pattern means. Before you call, it helps to note that pattern: three flashes might mean a pressure switch problem, for example, while a different sequence points to a flame failure. Passing that along lets us bring the most likely parts.
If there is no light at all, the furnace may not have power. Check the service switch near the unit and the breaker in the panel. A blown low-voltage fuse on the control board is another possibility we test for.
The repairs we make most often
Furnaces have a handful of parts that wear out far more often than the rest.
- Hot surface igniter: brittle by design and prone to cracking with age; a cracked one simply never glows.
- Flame sensor: a thin rod that builds up residue and stops confirming the flame, causing burners to light then shut off.
- Pressure switch and hoses: a switch that fails to close, often because of a cracked hose, a blocked vent or a full condensate trap.
- Inducer motor: noisy bearings or a motor that will not start, which stops the startup sequence at step one.
- Blower motor and capacitor: the burners heat but no air moves, and the furnace shuts down on the high-limit switch.
- Limit switches: tripping because of poor airflow from dirty filters, closed vents, or undersized return air.
Airflow and older ductwork
Overheating is a frequent underlying cause in older South Pasadena homes. If the return grille is small or the ducts are restricted, the furnace cannot move enough air across its heat exchanger, the temperature inside the cabinet climbs, and the limit switch shuts the burners down. Over many seasons, repeated overheating stresses the heat exchanger itself. When we see limit trips, we measure static pressure and temperature rise, and if airflow is the root issue we say so, even if the immediate repair is just a new filter or switch.
Our safety routine on every repair
Because a furnace burns natural gas inside your home, we never treat a repair as finished just because heat comes out of the vents. We inspect the heat exchanger for visible cracks or corrosion, confirm the flue connections are tight and drafting correctly, check the gas pressure at the valve, and measure carbon monoxide near the appliance. If something is unsafe, we explain what we found and turn off the gas to the furnace instead of leaving it running. We also encourage every household with gas appliances to keep a working carbon monoxide alarm near the bedrooms.
If replacement comes up
Sometimes the honest answer is that the furnace has reached the end. A cracked heat exchanger or a unit with parts no longer available may not be worth fixing. Replacement in this region involves an extra consideration: South Coast AQMD Rule 1111 limits NOx emissions from natural-gas central furnaces sold and installed here, and the district has been amending the rule toward zero-emission requirements, with compliance dates it sets and revises. Anyone planning a new furnace should check the current rule, and we can explain how it shapes your choices, including heat pumps as an alternative. We also repair furnaces in Alhambra, San Marino, San Gabriel, Monterey Park and Rosemead.
More services in South Pasadena
- AC Repair in South Pasadena
- Heating Repair in South Pasadena
- Heat Pump Installation in South Pasadena
- AC Installation in South Pasadena