Furnace Not Heating in San Ramon, CA

Furnace Not Heating in San Ramon

San Ramon gets genuine cold by Bay Area standards. Overnight lows of 35 to 40 in January mean the furnace earns its keep, and a no-heat call on a cold morning is one of the most urgent things we handle. The reassuring part is that it's almost always a single failed component. An igniter, a flame sensor, a limit switch tripped by a dirty filter, a gas valve, or a control board.

Most San Ramon furnaces we see are in the 1980s and 90s tract neighborhoods that make up the bulk of the city. Many of those original furnaces are now pushing or past 25 years. At that age they still fail in repairable ways most of the time, but heat exchanger cracks and dead control boards become more likely, so we check for them.

Our shop is at 365 Reflections Circle, on the Bishop Ranch side, so San Ramon is the city we reach fastest. On a no-heat call here we're typically a short drive away with the common furnace parts already on the truck.

Common causes

Cracked hot surface igniter. On the 1980s-90s tract furnaces across San Ramon, a cracked igniter is the most common no-heat cause. The ceramic element fails and stops lighting the burners. We test it, confirm it, and swap in the correct part, roughly $200 to $350, with heat restored the same visit.

Dirty or failing flame sensor. A carbon-fouled flame sensor lets the burner light then shuts it down seconds later, often cycling repeatedly on a cold morning. Cleaning the rod fixes most of these; a worn sensor gets replaced for $150 to $200. We check it early because it's cheap and frequent.

Limit switch tripped by a clogged filter. A neglected filter restricts airflow, the heat exchanger overheats, and the high-limit switch shuts the burners off. You get cold air despite the blower running. We replace the filter, verify airflow, and reset or replace the limit, usually a same-visit fix.

Gas valve not opening. When the igniter glows but the burners never light, the gas valve may be the issue. We check the valve coil, verify supply pressure, and rule out a closed manual valve. A failed valve is replaced and documented on the estimate.

Control board failure on a 25-plus-year unit. On San Ramon's aging tract furnaces, control board relays fatigue and the system won't sequence ignition. We meter the board before condemning it. On a furnace this old, a burned board is also a signal to run the replacement math, because at 25-plus years a heat pump conversion often makes more sense than a major part.

Cracked heat exchanger (CO safety). We test CO and inspect the heat exchanger on every gas call, and on San Ramon's older furnaces a crack is a real possibility. If we confirm one on camera, we shut the system down and show you the footage. At that age, conversion to a heat pump usually beats repair, and we put any rebates that currently apply on the written estimate so you can compare.

How we diagnose it

Thermostat call for heat and board wiring before opening the cabinet
Igniter glow and continuity, then flame sensor signal across a firing cycle
Filter, airflow, and the high-limit switch for an overheat trip
Gas valve operation and supply pressure when the igniter glows but burners don't light
CO and heat exchanger condition by camera on every gas furnace, especially the 25-plus-year units

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

Furnace Not Heating in San Ramon: common questions

How quickly can you get to a no-heat call in San Ramon?

Faster than anywhere else, because our shop is here at 365 Reflections Circle. San Ramon is the closest city to our base, and we carry the common furnace parts, igniters, flame sensors, and capacitors, on the truck, so a lot of no-heat calls get fixed on the first visit. We'll give you an honest arrival window when you call.

My San Ramon furnace is 25 years old and just failed. Repair or replace?

At 25-plus years, it depends on what failed. A cracked igniter is a clear repair. A cracked heat exchanger or a burned control board usually tips toward replacement. We put both the repair and replacement numbers on the written estimate, along with any rebates that currently apply, so you can decide with real figures rather than a guess.

It's 38 degrees out and my furnace blows cold air. What's the likely cause?

Cold air with the blower running usually means the burners aren't lighting or aren't staying lit. A cracked igniter, a dirty flame sensor, a tripped limit switch from a clogged filter, or a gas valve that isn't opening. All four are repairs. We diagnose the exact one before quoting, and on a cold night we prioritize the call.

Nearby and related

Furnace Not Heating near San Ramon: Danville · Alamo · Dublin · Pleasanton .

This is usually a furnace repair in San Ramon job. See our furnace repair overview or the San Ramon service area.