Furnace Not Heating in Castro Valley
Castro Valley sits between the bay's cool air and the inland warmth, so the furnace gets worked hard enough in winter to surface problems. When it stops heating, the system usually still tries to run, it just can't complete ignition or hold the flame. The housing here is mostly mid-century ranches, and a lot of the equipment is on its first or second replacement and well past 15 years.
On furnaces of that age the cause is almost always a single part. Hot surface igniter cracks and flame-sensor carbon buildup are the two we see most on older Castro Valley gas furnaces, the failure modes that look like a dead furnace but are a couple hundred dollars to fix. A limit switch tripped by a clogged filter is close behind, and the original ductwork in many of these homes is leaky and poorly insulated, which makes airflow problems more common than they should be.
We diagnose the actual failure before talking replacement. If the furnace itself is sound and the fix is an igniter, we say so. If it is an old unit with a cracked heat exchanger, that is a different conversation and we show you the evidence.
Common causes
Cracked hot surface igniter. The most common no-heat failure on Castro Valley gas furnaces. The igniter cracks from years of heat cycling and stops glowing, so the burners never light. You hear it try and fail. We confirm with a continuity test and replace it.
Carboned flame sensor. The furnace lights and shuts off within seconds because the carbon-coated sensor can't prove the flame, so the board closes the gas for safety. Cleaning it usually restores normal operation. We replace it only if it's pitted.
Limit switch tripped by a dirty filter or leaky ducts. Restricted airflow overheats the heat exchanger and the limit switch shuts the burners down. With the poorly insulated, leaky ductwork common in these older homes, airflow problems show up often. We check the filter, test the ducts, and confirm the switch resets and holds.
Control board failure. On aging equipment the board can lose the relay that runs the ignition sequence. We read the fault code and trace the sequence to confirm the board is the real failure, not a wiring or sensor issue feeding into it.
Cracked heat exchanger on the oldest units. On original furnaces well past their service life, a no-heat call sometimes uncovers a cracked heat exchanger, which is a CO safety issue. We inspect with a camera and show you the crack. That usually means replacement, and we run the numbers honestly.
Blower motor failure. Burners light but no warm air reaches the rooms because the blower motor or its capacitor has quit. We test the windings and the capacitor and confirm operation on the heating speed.
How we diagnose it
- Confirm the thermostat is calling and the furnace has power and gas.
- Watch the ignition sequence and read the board's fault code.
- Check the filter and test the ductwork for leakage that starves airflow.
- Run combustion analysis, CO testing, and a heat exchanger inspection on any older unit.
- Put the part, the price, and any replacement math on a written estimate before we proceed.
$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.
Furnace Not Heating in Castro Valley: common questions
Do you cover Castro Valley from your San Ramon base?
My furnace is original to the house. Repair or replace?
The furnace tries to light, clicks, and gives up. What is that?
Nearby and related
Furnace Not Heating near Castro Valley: San Leandro · Hayward · Dublin .
This is usually a furnace repair in Castro Valley job. See our furnace repair overview or the Castro Valley service area.
Furnace Not Heating in Castro Valley
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