Furnace Not Heating in Los Gatos, CA

Furnace Not Heating in Los Gatos

A furnace that won't heat is almost always one failed part in a lighting sequence, not a system that's done. The igniter has to glow, the gas valve has to open, the flame sensor has to confirm the burn, and the limit switch and board have to allow it. When one of those fails, heat stops, and the fix is usually a single component.

Los Gatos makes the diagnosis interesting because the housing is so varied. The hillside customs tend to run multi-zone forced air, so 'no heat upstairs' often traces to a zone damper or board rather than the furnace. Older homes closer to downtown are different. Some still run standing-pilot or older gas furnaces, where no-heat can mean a fouled pilot, a failing thermocouple, or a unit near the end of its life. We figure out which kind of system you have before we quote.

Heating demand here is mild, so a December no-heat call is rarely dangerous. The real risk on the older units is carbon monoxide from a cracked heat exchanger, which is exactly why we test for both on every gas call.

Common causes

Cracked hot surface igniter. On the modern furnaces in the hillside homes, a cracked igniter is the number one no-heat cause. It glows to light the burners and fails from years of heat cycling. We ohm it out, confirm the crack, and replace it. The part cost goes on your written estimate.

Flame sensor carbon buildup. Furnace fires, then dies after a few seconds. The flame sensor is coated and the board can't confirm flame, so it shuts the gas off. Cleaning the rod fixes it most of the time. If the sensor is worn out, a replacement is a small part we'll price for you first.

Pilot or thermocouple on older units. Some older homes here still have standing-pilot furnaces. No heat there usually means the pilot won't stay lit, which points to a dirty pilot orifice or a failing thermocouple. We can often restore these, but on a unit well past its service life we'll be straight with you about whether a repair makes sense or a ductless conversion is the better money.

Limit switch tripped by restricted airflow. A clogged filter or partially closed registers chokes return air and overheats the furnace, tripping the high-limit. This shows up often when a home gets reconfigured and the airflow never gets rebalanced. We replace the filter, check static pressure, and confirm the limit resets before calling it fixed.

Zone board or stuck damper. On multi-zone hillside systems, one cold wing while the rest of the house heats usually means a failed zone board or a damper stuck shut. We meter board outputs and manually cycle dampers to isolate it. The furnace itself is frequently fine.

Cracked heat exchanger. On older furnaces we sometimes find a cracked heat exchanger during the safety check. That's a CO risk, not a normal repair. We show you the crack on camera before quoting, and if CO is dangerous we shut the unit down before leaving and document it.

How we diagnose it

Identify the system type first: modern forced air, multi-zone, or an older standing-pilot furnace, since each fails differently.
Watch the full ignition sequence to pinpoint where heat stops, igniter, flame sensor, gas valve, or blower.
On multi-zone homes, meter the zone board and cycle dampers to separate a controls problem from a furnace problem.
Check filter and static pressure to catch airflow-driven limit trips.
Run CO testing and inspect the heat exchanger on every gas furnace, especially the older units.

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

Furnace Not Heating in Los Gatos: common questions

Are you local to Los Gatos or coming from far off?

We're a San Ramon shop that covers the South Bay regularly, Los Gatos included. Hillside addresses can add drive time, so we'll give you a realistic arrival window when you call rather than promising same-day and missing it.

My downtown home has an old standing-pilot furnace. Repair or replace?

Depends on age and the heat exchanger. If an older standing-pilot unit has a no-heat fault plus a cracked exchanger, repair rarely pays. In a home with no usable ductwork, a multi-head ductless system is often the cleaner answer. We run the numbers at the estimate before you decide.

Only the upstairs is cold. Is the furnace broken?

Probably not. On a multi-zone hillside home, one cold floor usually means a zone damper stuck closed or a failed zone control board, while the furnace heats the rest of the house fine. We isolate it at the board before touching the furnace.

Nearby and related

Furnace Not Heating near Los Gatos: Saratoga · San Jose · Cupertino .

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