Furnace Not Heating in Concord

Furnace Not Heating in Concord

Concord runs hot in summer, but the furnace still matters in winter, and when it stops heating it tends to do so quietly until the first cold morning when everyone notices at once. The pattern is the same on most calls: the thermostat calls, the system tries to start, but the burners never light or the heat never reaches the rooms. The good news is that this is rarely a dead system. It is usually one failed part.

Most Concord housing is older tract construction, and many of these systems are in their second or third replacement cycle. On gas furnaces past their early teens, the recurring no-heat causes are a cracked hot surface igniter, a carboned flame sensor, or a limit switch tripped by a dirty filter. Each is a defined repair, not a reason to replace the furnace.

We also see oversized furnaces in a lot of the tract installs around here, and an oversized unit short-cycles, which wears parts out faster than they should. When we do replace, we run a Manual J load calculation instead of matching the old tonnage. But for a straight no-heat call the first job is finding the one part that failed and fixing it.

Common causes

Cracked hot surface igniter. The most common modern no-heat failure. The igniter cracks from heat cycling and stops glowing, so the burners never light. We confirm with a continuity test and replace it, then watch a clean ignition cycle.

Dirty flame sensor. The furnace lights and then dies within seconds because the carboned sensor can't prove the flame, so the board cuts the gas for safety. Cleaning the sensor usually fixes it. Replacement only if it's degraded.

Limit switch tripped by a clogged filter. Restricted airflow overheats the heat exchanger and the limit switch shuts the burners off to protect it. People read it as a dead furnace. We check the filter, clear the restriction, and confirm the switch resets.

Short-cycling damage on oversized units. An oversized furnace short-cycles, which wears igniters, sensors, and boards prematurely. We fix the failed part now and flag the sizing problem so it gets addressed at the next replacement with a proper load calc.

Control board failure. An aging board can lose the relay that drives the ignition sequence, leaving the furnace dead even with good parts downstream. We read the fault code and confirm the board is the actual failure, not a wiring or sensor issue.

Failed gas valve. On older equipment the valve can fail to open even with a glowing igniter and a clean sensor. We measure the valve coil and inlet gas pressure before condemning it, since an upstream fault can mimic a bad valve.

How we diagnose it

• Confirm the thermostat is calling and the furnace has power and gas supply.
• Watch the full ignition sequence and read the control board fault code.
• Check the filter and airflow for a limit-switch trip, and note any short-cycling.
• Run combustion analysis and CO testing, and inspect the heat exchanger.
• Write the failed part, the price, and any sizing concern on an estimate before the repair.

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

Furnace Not Heating in Concord: common questions

Nearby and related

Furnace Not Heating near Concord: Walnut Creek · Martinez .

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