Furnace Blowing Cold Air in Berkeley

Furnace Blowing Cold Air in Berkeley

Berkeley's climate is mild and coastal, which means AC is rarely the priority but heating very much is. When a Berkeley furnace runs and blows cold air, the blower is working and the heat side has failed. On the older gas furnaces common in the flats bungalows and the hillside homes, that is almost always one worn part, not a system at the end of its life.

The most frequent cause we find is a cracked hot surface igniter or a flame sensor fouled with carbon, so the burners light and then drop out. The board shuts the gas when it loses flame confirmation, while the blower keeps running and pushes unheated air. Both are inexpensive single-part repairs.

Berkeley's housing stock skews old, and a lot of these furnaces are well into their second decade. On equipment that age we also run combustion analysis and CO testing while we are on site. If a furnace is cold because the burners keep cutting out, we want to know whether it is a tired igniter or something on the safety side before we hand back a clean bill.

Common causes

Cracked hot surface igniter. Common on the aging gas furnaces in Berkeley homes. The igniter weakens, the burners fail to stay lit, and the blower delivers cold air. We test igniter resistance, watch the ignition cycle, and replace it, usually $200 to $350.

Flame sensor fouled with carbon. On an older furnace the sensor carbons up and the board can no longer confirm flame, so it shuts the gas. Cleaning the rod usually restores it; a worn sensor is $150 to $200 to replace.

Thermostat fan set to ON. Set to ON, the blower runs constantly and blows room-temperature air between heating cycles, which feels like a broken furnace. We confirm the setting first. No part needed.

Overheating limit short-cycling. A clogged filter or restricted return in a tight old Craftsman makes the furnace overheat, and the high-limit shuts the burners while the blower runs to cool the heat exchanger. That cold blast is the tell. We clear the restriction and verify the limit cycles correctly.

Pilot or gas valve issue on older units. On the oldest Berkeley furnaces a finicky pilot or a tired gas valve can stop the burners from staying lit. We test the valve and ignition system and, on units this old, fold it into a full combustion and CO check.

Aging control board. On a furnace well past its first decade the board can intermittently drop the burner circuit while keeping the blower on. We confirm the board as the actual fault before replacing it, since wiring and sensors mimic the same symptom.

How we diagnose it

• Confirm the thermostat is calling for heat and the fan is set to AUTO.
• Watch a full ignition cycle and test the igniter and flame sensor.
• Run combustion analysis and CO testing on the gas furnace, which we do as part of these older-unit calls.
• Check filter and return airflow, then verify the high-limit switch opens and closes correctly.
• Inspect the gas valve and control board if ignition checks out.

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

Furnace Blowing Cold Air in Berkeley: common questions

Nearby and related

Furnace Blowing Cold Air near Berkeley: Oakland · Richmond .

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