Furnace Not Heating in Mountain View, CA

Furnace Not Heating in Mountain View

Mountain View summers are mild enough that a lot of the older housing stock around the downtown core was built with heat only, no central AC, so the gas furnace is the one piece of mechanical equipment the house leans on. When it stops making heat, you notice fast. The good news is that a furnace that blows cold air or short-cycles is almost never a dead system. It is usually one part that has worn out or shut the system down on purpose.

Most no-heat calls we run here come down to ignition. A modern furnace lights with a hot surface ignitor, a small ceramic element that glows orange to light the burners. They crack with age and thermal cycling, and a cracked ignitor will not light. After that it is the flame sensor, which proves the flame is actually burning. When it gets coated in carbon the board reads no flame, shuts the gas, and you get a furnace that fires for a few seconds then quits, over and over.

On the 1940s through 60s homes around the downtown core, we also see limit switches tripping because a starved filter or a tight original duct run lets the heat exchanger overheat. That is a safety shutoff doing its job, not a failure. We test the actual cause before we touch parts.

Common causes

Cracked hot surface ignitor. The most common no-heat cause on furnaces built in the last 25 years. The ceramic element fails open and never glows, so the burners never light. We check it for continuity and visually for cracks, then replace it. Figure $200 to $350 depending on the unit.

Dirty flame sensor. Carbon buildup makes the board think the flame never lit, so it cuts gas a few seconds after ignition and tries again. The furnace fires and dies in a loop. Cleaning the sensor usually fixes it. If it is pitted past cleaning we replace it, $150 to $200.

Limit switch tripped by a clogged filter. Common in the older downtown ranches with tight original ductwork. A starved filter overheats the heat exchanger and the limit switch shuts everything down to protect it. We find the real restriction, replace the filter, and confirm airflow rather than just resetting it.

Failed inducer or pressure switch. The draft inducer pulls combustion gases out before the burners light. If the motor is worn or the pressure switch does not prove draft, the board will not allow ignition at all. We test the switch and motor amperage. Inducer replacement runs $400 to $700 on units past 12 years.

Thermostat or low-voltage wiring. On homes that have had AC added to an old heat-only furnace, the thermostat or its wiring is a frequent culprit, especially after a DIY swap. We meter the call-for-heat signal at the board to confirm whether the furnace is even being told to run before condemning anything inside it.

How we diagnose it

Watch a full ignition sequence at the furnace, inducer to ignitor to burner to flame proving, and note exactly where it stalls.
Test the ignitor for continuity and the flame sensor microamp reading against spec.
Check static pressure and the filter, since a starved system trips limits and mimics a part failure.
Meter the thermostat call and 24V control signal at the board to rule out a control problem before opening the gas train.
Run a CO test and inspect the heat exchanger before we sign off on any gas furnace.

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

Furnace Not Heating in Mountain View: common questions

Do you actually cover Mountain View, or are you based across the bay?

We are based in San Ramon and cover the whole Bay Area including the Peninsula and South Bay. Mountain View is a regular service area for us. Same-day is best effort, not a guarantee, but on a no-heat call we prioritize getting someone out. Call (925) 999-4095 and we will give you a real window.

My summers here are mild. Is it worth fixing the furnace at all, or should I just space-heat?

If the furnace is under 12 to 15 years old and the fix is an ignitor or flame sensor, repair is the easy call, you are spending a couple hundred dollars on a system that has years left. We only steer toward replacement when the heat exchanger is cracked or the unit is well past its service life. We run that math on the written estimate.

The furnace lights then shuts off after a few seconds. What is that?

Classic dirty flame sensor. The burners light, but the board cannot confirm flame, so it cuts the gas as a safety measure and retries. After a few lockout cycles it stops trying. Cleaning the sensor fixes it most of the time. Our $75 diagnostic is credited toward any repair over $200.

Nearby and related

Furnace Not Heating near Mountain View: Palo Alto · Los Altos · Sunnyvale .

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