The short answer
Most furnace failures in Los Altos come from the ignition chain: a dirty flame sensor, cracked igniter, stuck pressure switch or failing inducer. We diagnose the exact step that fails, repair it, and test for safe combustion and venting before the heat goes back on.
Winters in Los Altos rarely bring hard freezes, but the damp, chilly mornings between November and March are enough to make a silent furnace feel like an emergency. Gas furnaces here often run in short bursts for a few hours a day, and that start-stop pattern puts most of the wear on the ignition sequence: the igniter, flame sensor, pressure switch and inducer motor. ClearSky Heating & Cooling repairs furnaces across the 94024 area, traveling about ten miles west from our San Jose base. We trace the failure step by step, fix what is broken, and check the safety of the appliance before we leave.
How a Furnace Starts, and Where It Breaks Down
A modern gas furnace runs through a fixed sequence each time the thermostat calls for heat. Knowing that sequence helps explain why one small part can stop the whole unit, and why the control board's blinking light is a useful clue.
- Thermostat calls for heat and the control board wakes up
- Inducer motor starts to clear the heat exchanger and draw combustion gases out the vent
- Pressure switch confirms the vent is drawing properly
- Hot surface igniter glows, or a spark igniter fires
- Gas valve opens and the burners light
- Flame sensor confirms flame; if it cannot, the board shuts the gas off within seconds
- Blower starts and pushes warm air through the ducts
Failures We Fix Most Often
A furnace that lights, runs for a few seconds, then shuts down and tries again is almost always a flame sensor problem. A thin layer of oxidation keeps it from reading the flame, and cleaning or replacing it is quick. A furnace that clicks and hums but never lights may have a cracked igniter, a stuck pressure switch, or a vent or condensate blockage on a high-efficiency model.
Blower issues show up differently: the burners light, but little or no air comes from the registers, or the furnace overheats and trips its limit switch. A failing blower motor, a bad capacitor, or a severely clogged filter can each cause that. We confirm the cause with meters and the board's fault codes rather than swapping parts until something works.
Safety Comes Before Comfort
Every furnace repair visit includes a check of combustion and venting. We look at the flue connection, test for proper draft, inspect the burners and flame pattern, and examine the heat exchanger for cracks or heavy corrosion. A cracked heat exchanger can let combustion gases mix with the air your family breathes, so if we find one, we will tell you directly and shut the furnace off rather than leave it running.
If your carbon monoxide alarm sounds, leave the house, call the gas utility or 911 from outside, and do not restart the furnace. Once the home is cleared, we can find the source. Homes in this area with older furnaces in closets or attics benefit from working CO alarms on every level.
Repair Now, Plan for Later
Homeowners sometimes ask whether new Air District rules mean they must replace a furnace now. They do not. The Bay Area Air District appliance rules apply only when a furnace fails or is replaced, and they do not force anyone to remove working equipment. Keeping a sound furnace running with good repairs is a perfectly reasonable choice.
What the rules do change is the long view. Gas furnaces manufactured from 2029 must meet a zero-NOx emission standard, which in practice points replacements toward heat pumps. If your furnace is old and repairs are getting frequent, we can price a heat pump alongside the repair so you can decide on your own timeline.
A Short Pre-Winter Checklist
Before the first cold snap, swap the furnace filter, make sure nothing is stored against the furnace or blocking the return grille, and test your thermostat by raising the setpoint a few degrees. If you smell a brief dusty odor on the first run, that is normal; a persistent burning or gas smell is not. Booking a fall inspection lets us clean the flame sensor and test the igniter before they quit on a cold morning.
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