Furnace Not Heating in Danville

Furnace Not Heating in Danville

A furnace that fires up, runs the fan, and never gets warm is one of the most common winter calls we get in Danville. Overnight lows here sit around freezing in January, so when an older forced-air unit quits, the house cools off fast. Owners assume the worst. In practice the furnace is almost always one part short of working. The usual suspects are a cracked igniter, a flame sensor coated in carbon, or a limit switch that tripped because the filter is choked.

What we find shifts with the equipment. A lot of older Danville homes run gas furnaces that are well past their prime, where the failure is usually a worn ignition component. Newer and higher-end homes often run multi-zone systems with control boards and zone dampers, and a no-heat call on that kind of setup is more likely a control or staging fault than a simple igniter. We diagnose to the part before we quote, so the written estimate names the actual failure.

None of this means you need a new system. A furnace that has heated reliably for years does not quit all at once. It loses one component, and most of those are a same-visit fix.

Common causes

Cracked hot surface igniter. This is the single most common no-heat cause on Danville gas furnaces. The igniter glows to light the burners, and after years of heat cycling the element cracks and stops glowing. We test it for continuity and inspect it under light. It is usually replaced on the first visit, and the part and labor go on the written estimate before we start.

Dirty flame sensor. The furnace lights, then shuts down a few seconds later, and cold air follows. A carbon-fouled flame sensor stops proving the flame, so the control board kills the gas as a safety. Cleaning the sensor often restores heat. If it is pitted past cleaning we replace it, and we tell you which one it is before charging for a new part.

Limit switch tripped by a clogged filter. Restricted airflow lets the heat exchanger overheat, and the limit switch shuts the burners down to protect it. We see this often in older homes with tight return ducting. We check the filter, the blower, and the switch, then confirm the unit holds temperature through a full cycle once airflow is restored.

Control board or staging fault. On multi-zone systems, a failing control board or a stuck zone damper can leave the furnace calling for heat but never delivering it. We read the board fault codes and test the staging sequence rather than guessing. This is where the diagnostic time earns its keep.

Failed draft inducer motor. If the inducer does not spin up, the pressure switch never closes and the furnace will not let the burners light at all. Common on older systems. We confirm the failure with the pressure switch reading before we quote the motor on the estimate.

Thermostat or wiring issue. Sometimes the furnace is fine and the call for heat never reaches it. A dead thermostat battery, a loose C-wire, or a miswired smart thermostat shows up the same as a furnace failure. We rule this out early because it is cheap to fix and easy to miss.

How we diagnose it

• We watch a full ignition cycle and note exactly where it fails: no igniter glow, flame then lockout, or burners that light while the blower runs cold.
• The control board fault codes come off first, and we check the filter and return airflow before condemning any part.
• Each suspect part gets metered. The igniter, flame sensor, limit switch, and pressure switch are tested, not swapped on a hunch.
• On every gas furnace call we run a carbon monoxide test and inspect the heat exchanger, because a no-heat symptom occasionally points to a cracked exchanger we will not let you keep running.
• Before we leave, we run the system through a complete heat cycle and verify it holds temperature.

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

Furnace Not Heating in Danville: common questions

Nearby and related

Furnace Not Heating near Danville: San Ramon · Alamo · Blackhawk · Walnut Creek · Pleasanton .

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