Furnace Not Heating in Milpitas

Furnace Not Heating in Milpitas

When a furnace stops producing heat, the system isn't usually dead. A gas furnace runs a fixed startup sequence. The inducer drafts, the igniter glows, the gas valve opens, the flame sensor confirms the burn, and the blower follows. One failed link stops heat entirely, and the fix is almost always a single part.

Milpitas homes lean on cooling. Summers run warm and households run the AC long hours, so the furnace side often gets ignored until the first cold snap. That's when a filter that's been clogged since summer finally trips the high-limit, or an igniter that's been on its last legs gives out. A fair amount of the newer stock runs multi-zone ducted systems, and we stock common ignition and control parts and have manufacturer warranty access for the major brands.

Winters here are mild, so a no-heat furnace is seldom an emergency. It is a good reason to clear the filter and run the safety check, since a furnace that's been overlooked all summer is exactly the kind that throws a limit fault or hides a CO problem on first firing.

Common causes

Cracked hot surface igniter. The most common no-heat failure on the modern furnaces around here. The igniter cracks from heat cycling and the burners never light, even though the blower runs. We ohm-test it, confirm the crack, and replace it, with the part cost on your written estimate.

Limit switch tripped by a clogged filter. Homes that run AC heavily all summer often have a filter that's been ignored for months. On the first heat call, the restricted airflow overheats the furnace and trips the high-limit, killing the burners. We replace the filter, check static pressure, and confirm the reset. This is one of the most preventable no-heat calls we get from Milpitas.

Flame sensor carbon buildup. Furnace lights, then shuts off seconds later. The flame sensor is fouled and the board can't confirm flame. Cleaning the rod usually fixes it. If it's worn out, replacing it is a small part we'll price first.

Zone damper or control board on multi-zone homes. Larger homes with multi-zone ducted systems can go cold in one area while the rest heats fine. That's usually a stuck damper or a zone board, not the furnace. We meter the board and cycle dampers to isolate it, and re-balance airflow if it drifted.

Gas valve not opening. Igniter glows, inducer runs, but no burners. The gas valve may not be opening. We verify gas pressure and the control signal before replacing it, since a wiring or board fault can imitate a bad valve.

Cracked heat exchanger. On furnaces approaching the older end of the local housing stock, we check the heat exchanger for cracks, a carbon monoxide hazard. We show you any crack on camera before quoting, and shut the system down if CO levels are unsafe.

How we diagnose it

• Confirm the thermostat is calling for heat and the furnace board is getting the signal.
• Run the full ignition sequence to find where heat actually stops.
• Inspect and replace the filter, then measure static pressure, the usual culprit after a long cooling season.
• On multi-zone homes, meter the zone board and cycle dampers to separate controls from furnace.
• Test CO and inspect the heat exchanger on every gas furnace before we sign off.

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

Furnace Not Heating in Milpitas: common questions

Nearby and related

Furnace Not Heating near Milpitas: Fremont · Newark .

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