The short answer
Furnace repair in Atherton usually means fixing an igniter, flame sensor, pressure switch, inducer motor or control board. We test the heat exchanger and venting on every visit, and a working furnace can legally be repaired and kept running.
A furnace that clicks, tries to light and then gives up on a damp January morning is one of the most common winter calls we take from Atherton. ExpertFlow HVAC Repair Service travels about nine miles from our Los Altos base to San Mateo County homes in ZIP 94027 to repair gas furnaces of every age, from tidy modern units in a garage closet to older equipment tucked into a crawlspace or attic. This page covers how we approach furnace problems specifically, what the warning signs mean, and how current Air District rules affect a repair decision.
The ignition sequence, and where it breaks
A gas furnace follows the same steps every time it starts: the thermostat calls, the inducer fan purges the heat exchanger, a pressure switch confirms the vent is clear, the igniter glows, the gas valve opens, and the flame sensor proves the burners lit. Most failures happen at one of those steps, and the control board's blink code usually points to which one.
That is why our first move is to watch a full cycle and read the board rather than guess. A dirty flame sensor that shuts the burners off after a few seconds needs a cleaning, not a new board. A cracked hot surface igniter needs replacement. A pressure switch fault can mean a failing inducer, a blocked vent, or condensate backing up in a high-efficiency unit.
Signs your furnace needs attention
Call for service, rather than waiting for a full breakdown, if you notice any of these:
- Burners light, then shut off within seconds, again and again
- A yellow or lazy flame instead of a steady blue one
- Rumbling, booming or screeching from the cabinet at startup
- A carbon monoxide alarm sounding, or headaches that ease when you leave the house
- Rooms far from the furnace staying cold while the closest ones overheat
- The blower running nonstop even when the thermostat is satisfied
Safety checks we never skip
Every furnace repair includes a look at the parts that keep combustion gases out of your living space. We inspect the heat exchanger for cracks or rust-through, check the flue for proper slope, connections and draft, and measure carbon monoxide at the appliance. In older Atherton homes, venting has sometimes been modified during remodels, and a vent that once worked can end up undersized or disconnected.
If we find a condition that is unsafe, we explain it, show you what we saw, and shut the gas to the furnace if needed. We would rather have an uncomfortable conversation than leave a hazard running.
Airflow problems that look like heating problems
Not every cold room means the burners are at fault. A furnace can light perfectly and still leave a bedroom chilly if the blower motor is weak, the filter is packed with dust, or a duct has slipped off a fitting in the attic. On long, branching duct systems the farthest rooms are the first to suffer. We measure temperature rise across the furnace and static pressure in the ducts to separate a combustion issue from a delivery issue.
High-efficiency furnaces add one more possibility: they produce water, and a clogged condensate trap or line will trip a safety switch and stop the heat. That fault often shows up after a long idle summer, when residue has dried in the trap. Clearing it takes a few minutes, but finding it requires knowing where to look, especially when the furnace sits in a cramped attic platform.
Repair, or plan for something else?
Most furnaces are worth repairing. The Bay Area Air District rules do not require anyone to replace working equipment; they apply only when a furnace fails or is replaced. When replacement does come up, keep in mind that under Rule 9-4, gas furnaces manufactured from 2029 must meet a zero-NOx standard, which in practice points toward heat pumps.
So if your furnace is old, has a damaged heat exchanger, or needs a string of expensive parts, we lay out both paths: a new furnace now, or a heat pump that also provides cooling. BayREN and local clean energy providers sometimes fund electrification projects; we verify current offers before quoting them. The federal 25C credit ended for systems placed in service after 2025.
Keeping a repaired furnace reliable
Winters on the mid-Peninsula are mild and damp rather than harsh, so furnaces cycle often at low demand. That is gentle on the heat exchanger but hard on igniters and flame sensors. A fall check that cleans the burners and sensor, tests the safety switches and replaces a clogged filter goes a long way.
We also repair furnaces in Menlo Park, Palo Alto, Portola Valley, Los Altos Hills and East Palo Alto, so a single call covers a second property nearby.
More services in Atherton
- AC Repair in Atherton
- Heating Repair in Atherton
- Heat Pump Installation in Atherton
- AC Installation in Atherton
