Furnace Not Heating in Los Altos Hills

Furnace Not Heating in Los Altos Hills

When a furnace stops producing heat, it's almost always one part in the ignition or safety chain rather than a failed system: a cracked hot surface igniter, a carboned flame sensor, a limit switch tripped by a dirty filter, or a control board that dropped a relay. On the large, spread-out homes in Los Altos Hills, that single failure tends to take out one zone or one wing while the rest of the house keeps running.

These are one-acre-minimum lots on rolling foothill ground, and the floor plans are big enough that a single furnace rarely serves the whole house. More than one air handler, and zoning to go with it, is common. So a no-heat call here usually means tracing which system is down, then which part inside it failed. The foothill climate runs warmer and drier than the bayside towns, and the winter mornings are cool enough that you notice fast when a zone quits.

The ground adds its own constraints. Equipment sits where the grade allows, line sets run long across these wide plans, and a fair number of these properties are on septic. We plan the visit around the property, not the furnace alone. The actual repair, though, is usually a contained part-level fix once we've found the right unit.

Common causes

Cracked hot surface igniter. The most common reason a forced-air furnace never lights. The igniter cracks from repeated heat cycling and stops glowing. We meter it for continuity and replace it, $200 to $350. When a home runs more than one unit, the oldest usually fails first.

One zone's system down. With the house spread across a large lot and more than one air handler, a no-heat complaint is often one wing out. We identify which system serves the cold area and diagnose that unit specifically, leaving the working zones alone.

Dirty flame sensor. Lights then quits after a few seconds: the sensor is carboned and the board can't confirm flame, so it cuts gas as a safety. Cleaning usually restores it; a pitted sensor runs $150 to $200 to replace.

Limit switch tripped by a clogged filter. On a big house with several returns, one filter gets forgotten, airflow chokes, the heat exchanger overheats, and the high-limit shuts the burners down. We confirm filter condition and airflow and check whether the limit reset or failed.

Stuck zone damper. A damper that won't open leaves a wing cold even while the furnace fires. On these spread-out zoned plans that's a common false alarm. We test the damper motors and zone panel to separate a distribution issue from a heat-production failure.

Control board or zone-board fault. Where systems age at different rates, a heat relay or zone board can fail and stop one system from delivering heat. We test board outputs before condemning it, since the board is one of the more expensive furnace parts.

How we diagnose it

• Confirm a real heat call reaches the affected system, then isolate which air handler serves the cold wing.
• Run the full ignition sequence and meter igniter, flame sensor, and limit switch on that furnace.
• Separate a heat-production fault from a stuck zone damper or blower issue.
• Test control and zone board outputs before condemning costly boards.
• Meter carbon monoxide and inspect the heat exchanger on the affected gas furnace before leaving.

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

Furnace Not Heating in Los Altos Hills: common questions

Nearby and related

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

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