The short answer
Most Los Altos furnace failures happen at a specific step of the startup sequence, often a dirty flame sensor, a failed igniter, a stuck pressure switch or a clogged filter tripping the limit switch. A technician tests each stage in order to find the fault and checks for safety issues such as a cracked heat exchanger.
Winters in Los Altos are mild and damp rather than harsh, so a gas furnace here may sit untouched from April through October. The first chilly morning of the season is when many owners discover a problem: the blower comes on but blows cool air, the burners light and then go out, or nothing happens at all. EliteAir Heating & Cooling repairs gas furnaces throughout 94024, driving over from our San Jose base about 11 miles to the east. Below is how a furnace is supposed to start, where that sequence tends to break, and what we look for when we open the cabinet.
The startup sequence, step by step
A modern gas furnace follows the same routine every time the thermostat calls for heat. Knowing that routine makes the repair less mysterious, because a failure at any one step stops everything after it.
First, the control board starts the draft inducer motor, which pulls air through the heat exchanger and out the vent. A pressure switch confirms the vent is clear. Next, a hot surface igniter glows, the gas valve opens and the burners light. A flame sensor proves the flame within a few seconds; if it cannot, the board shuts off the gas. Once the heat exchanger warms, the main blower starts and pushes warm air through the ducts. Throughout the cycle a high limit switch watches for overheating.
Where Los Altos furnaces usually fail
Long idle months and dust buildup cause predictable trouble. These are the faults our technicians find most often:
Age plays a role too. Igniters and flame sensors are wear items that most furnaces need replaced at some point, and a furnace that sat through a dusty summer remodel may arrive at the first cold week with a filter and burner area that need cleaning before anything else. Before swapping parts, our technician reads the control board's fault code, since most modern furnaces store a blink pattern that points to the failed stage. That one step often separates a quick repair from an afternoon of guesswork, and it lets us show you exactly why a part was replaced.
- Flame sensor coated with residue, so burners light and then shut off after a few seconds
- Cracked or burned-out hot surface igniter, leaving the furnace unable to light
- Pressure switch or inducer problems caused by a blocked vent, a cracked hose or condensate in the line
- High limit trips from a clogged filter or closed registers that trap heat in the cabinet
- Blower motor or capacitor failure, so the burners run but warm air never reaches the rooms
- Thermostat wiring or batteries, which can mimic a furnace failure completely
Safety comes before comfort
A furnace burns natural gas inside your home, so every repair visit includes safety checks. We inspect the heat exchanger for cracks or rust-through, confirm the vent is drafting properly, and test for carbon monoxide around the appliance. Older furnaces in garages, closets and attics can develop venting issues as connectors corrode or get bumped during storage.
If you smell gas, leave the house and call the gas utility from outside before calling us. If a carbon monoxide alarm sounds, get everyone outside and call 911. Those situations come first; the furnace repair can wait until the home is confirmed safe.
Repairing versus replacing an older furnace
Repairing a furnace keeps it in service, and Bay Area Air District appliance rules do not require replacing working equipment. Those rules apply only when an existing furnace fails or is replaced. That said, under Rule 9-4, natural gas furnaces manufactured from 2029 must meet a zero-NOx standard, which effectively steers future replacements toward heat pumps.
So when your furnace is old and the repair is significant, a little planning helps. We can explain what the repair buys you in remaining life, and what a heat pump would involve for your specific house, so a future replacement happens on your schedule instead of during a cold snap. BayREN and your local clean energy provider post current electrification incentives, and we confirm the active offer before quoting anything.
Our service area near Los Altos
Along with Los Altos, we handle furnace repair in Los Altos Hills, Mountain View, Sunnyvale, Cupertino and Santa Clara. Calling early in the fall, before the first truly cold week, gives the most flexibility in scheduling and lets us catch a weak igniter or a dirty sensor before it leaves you without heat.
More services in Los Altos
- AC Repair in Los Altos
- Heating Repair in Los Altos
- Heat Pump Installation in Los Altos
- AC Installation in Los Altos