Furnace Blowing Cold Air in Piedmont

Furnace Blowing Cold Air in Piedmont

A Piedmont furnace that runs while the air stays cold has lost its heat output: the blower keeps circulating but the burners are not firing or holding. On the older forced-air systems common in Piedmont's early-century estate homes, that usually traces to a worn igniter or a dirty flame sensor. It is a single part, not a failed furnace.

Piedmont is mild and marine-influenced, so these furnaces run modestly through a cool winter. Light, intermittent use is exactly what lets a cracking igniter or a carboning sensor go unnoticed until the unit is asked to cycle on a cold night and cannot keep the burners lit. A furnace that heated last season and blows cold now has lost a component, not its core.

Piedmont's big multi-story Tudors and Colonials add a twist: these homes heat unevenly, with the top floor running warm and the ground floor cold, often on original ductwork that is tight for the square footage. That can make a real no-heat fault look like a comfort complaint, or the reverse. We separate the two by confirming whether the furnace is actually producing heat before we touch anything on the distribution side.

Common causes

Cracked hot surface igniter. The most common no-heat failure on these older furnaces. The igniter cracks from thermal cycling regardless of how mild Piedmont winters are. We confirm it never glows on a startup and test continuity, then replace it, typically $200 to $350.

Carboned flame sensor. If the burners light and then drop out within seconds, the flame sensor is not proving flame and the board shuts gas off. Carbon on the rod is the usual cause. We clean it, or replace a degraded rod for generally $150 to $200.

Thermostat fan set to ON. In a big Piedmont house with multiple thermostats or zoning, the fan left on ON runs the blower continuously and circulates cool air between cycles, which reads as cold registers. We check the settings first and confirm the furnace heats on a real call before opening it up.

High-limit trip from restricted airflow. When original ductwork runs tight for the square footage, a dirty filter or a restricted return overheats the heat exchanger and the high-limit cuts the burners while the blower runs. We check filter and static pressure, clear the restriction, and confirm the limit holds across a full cycle.

Uneven heat mistaken for no heat. A tall plaster-walled Piedmont house can run hot upstairs and cold downstairs on the same furnace, which feels like a cold-air problem on the lower floors. We verify the furnace is actually producing heat, then look at zoning and duct sizing as a separate comfort question rather than a repair.

Gas valve or supply fault. If the igniter glows and nothing lights, we meter gas to the valve and confirm it opens on command before condemning any gas part. We test, we do not guess.

How we diagnose it

• Confirm whether the furnace is actually making heat, separating a real fault from uneven multi-story distribution.
• Run a full startup and watch where it fails: igniter, burner light, flame proven, blower.
• Check every thermostat's fan setting in a multi-zone estate home.
• Test igniter continuity and flame-sensor signal, cleaning or replacing as needed.
• Inspect filter and measure airflow, since tight original ductwork makes a high-limit trip more likely.

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

Furnace Blowing Cold Air in Piedmont: common questions

Nearby and related

Furnace Blowing Cold Air near Piedmont: Oakland · Berkeley · Alameda .

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