Furnace Not Heating in Saratoga

Furnace Not Heating in Saratoga

Saratoga's heating load is mild, but the homes are big, and many run dual-zone systems with separate equipment for upstairs and downstairs. The practical effect on a no-heat call is that one zone can go cold while the other heats normally, which actually helps us isolate the failed unit quickly.

Even in these larger systems, no-heat almost always comes down to a single component. A cracked igniter, a fouled flame sensor, a limit switch tripped by a dirty filter, or a control board on one of the two furnaces. That's a repair on one zone, not a whole-house failure. We identify which system and which part before quoting anything.

These are homes people tend to stay in for a long time and expect long service life out of equipment, so when something fails we also tell you honestly where the unit sits in its lifespan. A repairable part on a well-maintained system is a clear fix. A furnace near the end of its life is a different conversation, and we lay out both on a written estimate.

Common causes

Cracked hot surface igniter on one zone. On a dual-zone home, an igniter usually fails on a single furnace, so one zone goes cold while the other works. We confirm which unit, test the igniter, and replace it with the correct part, roughly $200 to $350. Heat returns to that zone the same visit.

Dirty flame sensor. A carbon-fouled flame sensor lets the burner light then shuts it off within seconds, cycling on the affected zone. Cleaning the rod fixes most cases; a worn one is replaced for $150 to $200. We check it early because it's cheap and common.

Limit switch tripped by a clogged filter. These larger homes often run deep media filters, and a neglected one restricts airflow until the heat exchanger overheats and the limit switch cuts the burners. We replace the filter, verify airflow, and reset or replace the limit. On a dual-zone home we check both systems' filters.

Control board fault on one furnace. With two furnaces, a control board can fail on one and not the other. We meter the affected board for power and ignition sequencing before condemning it, because a failed sensor can mimic a dead board. We don't bill a board on a sensor problem.

Cracked heat exchanger on an aging unit (CO safety). On the older furnaces in these homes we test CO and inspect the heat exchanger on every gas call. A confirmed crack on camera is a safety shutdown for that unit. Because owners here keep their homes a long time, we'll talk through a replacement built for a long service life rather than a short-term patch.

Zoning damper or controller fault (mimics no-heat). In a zoned system, a stuck damper or a failed zone controller can make one area feel like the furnace died when the equipment is actually fine. We check the damper motors and zone board so we don't replace a healthy furnace part to chase a controls problem.

How we diagnose it

• Which zone and which furnace actually lost heat, on dual-system homes, before anything else
• Igniter glow and continuity, then flame sensor signal on the affected unit
• Filter and airflow on both systems, then the high-limit switch for an overheat trip
• Zone dampers and controller when one area is cold but the equipment appears healthy
• CO and heat exchanger inspection on every gas furnace, with camera footage on the older units

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

Furnace Not Heating in Saratoga: common questions

Nearby and related

Furnace Not Heating near Saratoga: Los Gatos · Cupertino · Los Altos .

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