Furnace Not Heating in Piedmont

Furnace Not Heating in Piedmont

A furnace that won't heat is, in nearly every case, one failed part rather than a dead system: a cracked igniter, a fouled flame sensor, a thermocouple that won't hold a pilot, a limit switch tripped by a starved filter, or a thermostat that lost its call for heat. Piedmont's housing stock makes the older end of that list especially likely.

Piedmont is almost entirely 1910s-to-1930s Tudor, Mediterranean, and Colonial estates set in the Oakland hills, and these houses were built for heat, not cooling. Many still run early forced-air or converted gravity furnaces that are well past their design life. On a system that old, a no-heat call often traces to a worn thermocouple on a standing pilot, a tired gas valve, or an igniter and board on a unit that was retrofitted along the way. The mild climate keeps cooling an afterthought here, but these homes lean hard on their heat through the winter, so a furnace going down gets noticed fast.

The architecture shapes the work. Plaster walls, balloon framing, and finished basements mean the furnace and its ductwork live in tight, awkward spots, and the original ducts are often undersized. When an old unit overheats and trips its limit, undersized ductwork is sometimes part of the story, beyond a dirty filter. We diagnose the part that failed and flag the airflow issue behind it.

Common causes

Worn thermocouple on a standing-pilot furnace. Many Piedmont homes still run older furnaces with a standing pilot. When the thermocouple weakens it stops generating the millivolts that hold the gas valve open, so the pilot won't stay lit and the burners never fire. We test its output and replace it, and on a unit this age we inspect the heat exchanger at the same time.

Cracked hot surface igniter. On the furnaces that have been retrofitted to electronic ignition, a cracked igniter is the common no-light failure. We meter it and replace it, $200 to $350. We confirm which ignition type the unit actually has before ordering parts.

Dirty flame sensor. Lights then shuts off within seconds: the flame sensor is carboned and the control can't confirm flame, so it cuts the gas. Cleaning usually restores it; a worn sensor is $150 to $200 to replace.

Limit switch tripped by undersized ducts or a dirty filter. These old homes often have undersized original ductwork. Combined with a clogged filter, airflow chokes, the heat exchanger overheats, and the high-limit shuts the burners down. We confirm filter and airflow and flag the duct sizing if it's the real cause, rather than just resetting the switch.

Failing gas valve on an aging unit. On furnaces decades old, the gas valve coil can weaken so it no longer opens reliably on a call for heat. We meter voltage at the valve and confirm whether it's the valve, the board feeding it, or the safety circuit upstream.

Heat exchanger crack on an old furnace. On a furnace this age, a cracked heat exchanger is a real possibility and a safety issue. We inspect it on camera and meter carbon monoxide. If we find a crack we show it to you before quoting, and a crack on a system this old usually points toward replacement, often a heat pump given the mild climate.

How we diagnose it

• Identify the ignition type first, standing pilot versus electronic, because that determines the whole diagnostic path on these older units.
• Watch a full heat cycle and test the thermocouple or igniter, flame sensor, gas valve, and limit switch directly.
• Confirm filter and airflow, and assess whether undersized original ductwork is overheating the unit.
• Inspect the heat exchanger on camera and meter carbon monoxide on every gas furnace, which matters most on equipment this old.
• Verify a real heat call reaches the controls before condemning any burner-side part.

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

Furnace Not Heating in Piedmont: common questions

Nearby and related

Furnace Not Heating near Piedmont: Oakland · Berkeley · Alameda .

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