Furnace Not Heating in Pacifica

Furnace Not Heating in Pacifica

No heat from a gas furnace almost always traces to one step in the ignition sequence failing. The inducer has to run, the igniter has to glow or spark, the gas valve has to open, and the flame sensor has to confirm the flame is lit, and a fault at any one of those steps shuts the whole cycle down as a safety measure. Add a tripped limit switch from restricted airflow, a dead thermocouple on an older wall or gravity furnace, or simply no call for heat reaching the board, and that covers nearly every no-heat call we run. We watch the sequence directly rather than swapping parts on a guess. The detail that matters in Pacifica is the marine layer that limits real cooling days and the salt air corroding outdoor equipment.

Housing age and local climate both matter on a no-heat call. Pacifica sits right on the ocean, and neighborhoods from Linda Mar to Rockaway Beach and Sharp Park all sit under a marine layer that holds through most summer days. Real cooling need is rare here. Heating and moisture control do the actual work. Housing spans older beach-adjacent cottages near Rockaway and Sharp Park to the larger Linda Mar valley tracts built from the 1960s on. Salt air off the ocean corrodes condenser coils, fan motors, and contactors faster here than almost anywhere inland, and the persistent damp raises the bar on drainage and moisture control.

In Pacifica, every gas furnace call includes a carbon monoxide reading and a heat exchanger check, regardless of what brought us out, because that's a safety step we don't skip. The written estimate covers the actual repair, and on an older furnace we'll tell you honestly whether a heat pump conversion is worth putting on the table too. The $99 diagnostic fee is credited toward the repair.

Common causes

Cracked hot surface igniter. The igniter is a thin ceramic element that eventually cracks from repeated heating and cooling cycles. Once it can no longer glow hot enough, the gas valve never gets confirmation to stay open.

Dirty flame sensor. A flame sensor coated with a thin layer of carbon can no longer read the flame properly, so the board shuts the gas valve seconds after ignition, over and over, until the furnace locks out.

Limit switch tripped by a dirty filter. Restricted airflow, often from a dirty filter, lets the heat exchanger run hotter than it should and trips the high-limit switch as a safety response, shutting the burners down. Older coastal homes here often have returns and duct runs sized for a mild climate that never expected much run time.

Failed thermocouple on a wall or gravity furnace. Older wall and gravity furnaces use a thermocouple rather than a flame sensor, and a weakening one shuts the pilot's gas valve even when the pilot is actually lit.

Corroded gas valve or board connection. Age and moisture take a toll on gas valve terminals and board connectors over time. The salt-laden coastal air here corrodes contacts, terminals, and coils noticeably faster than an inland climate would. That can cause an intermittent or complete no-heat fault.

Thermostat or no call for heat. If the call for heat never reaches the board, nothing downstream matters yet. We confirm 24 volts and a real heat call reach the furnace before assuming a mechanical failure.

How we diagnose it

• Confirm a real heat call reaches the control board, so we're diagnosing the furnace and not a dead thermostat or broken low-voltage wire.
• Watch a full ignition sequence: inducer, igniter glow, gas valve, flame sensing, and where in that chain it stops.
• Test the igniter, flame sensor, and limit switch directly with meters rather than swapping parts on a guess.
• On every gas furnace, meter carbon monoxide and inspect the heat exchanger; on older wall and gravity units this is non-negotiable.
• Check filter, airflow, and the gas valve and board connections. The salt-laden coastal air here corrodes contacts, terminals, and coils noticeably faster than an inland climate would. Older coastal homes here often have returns and duct runs sized for a mild climate that never expected much run time.

$99 diagnostic, credited toward the repair. You get a written quote before any work begins.

Furnace Not Heating in Pacifica: common questions

Nearby and related

Furnace Not Heating near Pacifica: Daly City · San Bruno · Half Moon Bay .

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