Furnace Not Heating in San Leandro

Furnace Not Heating in San Leandro

San Leandro's climate is mild on both ends, summer highs in the 70s and 80s near the bay, cool damp winters, so the furnace runs through the colder months and the system gets real use. When it stops making heat, it's usually one failed component. An igniter, a flame sensor, a limit switch tripped by a dirty filter, or a control board fault. That's a repair, not a replacement.

What makes San Leandro distinct is the housing. This is mostly mid-century suburban construction, and a lot of homes are on their second or third furnace while the ductwork underneath is still original. A no-heat call here sometimes uncovers a furnace that's fixable sitting on a duct system that has lost a chunk of its airflow to leaks over the decades.

We fix the immediate no-heat problem first. If we find the ducts are leaking badly while we're in there, we tell you, because it directly affects how well any furnace or future heat pump performs. But the priority on a cold day is getting heat back, and that's almost always a single part.

Common causes

Cracked hot surface igniter. The most common no-heat failure on the furnaces still serving these homes. The ceramic element cracks with age and stops glowing. We test it, confirm the failure, and install the correct replacement for your model, roughly $200 to $350. Heat is back the same visit.

Flame sensor carbon buildup. A fouled flame sensor makes the burner light and then cut out within seconds, sometimes cycling repeatedly. Cleaning the rod resolves most of these calls. If it's worn past cleaning we replace it, $150 to $200. It's one of the first things we check because it's cheap and frequent.

Limit switch tripped by a clogged filter. In these older homes with original returns, a neglected filter restricts airflow, the heat exchanger overheats, and the high-limit switch shuts the burners down to protect the system. You feel cold air. We replace the filter, confirm airflow, and reset or replace the limit. Often fixed in one visit.

Aging control board or relay. On systems past their first decade, board relays fail and the furnace won't sequence ignition. We meter the board's power and outputs before condemning it, since a bad sensor can mimic a dead board. We don't bill a board when the real fault is upstream.

Heat exchanger crack on an older unit (CO safety). On the older furnaces still in service here, we inspect the heat exchanger and test CO on every gas call. A confirmed crack is a safety shutdown, and we show you the crack on camera before discussing options. On a furnace this old, replacement, often a heat pump, usually makes more sense than chasing it.

Duct leakage starving the system. Original mid-century ductwork that's lost integrity won't stop the furnace from lighting, but it makes the house never feel warm even when the furnace is healthy. We test the ducts on the estimate. If they're leaking enough to matter, sealing them recovers real performance. We flag it but never let it delay the no-heat fix.

How we diagnose it

• Thermostat call for heat and wiring at the board before opening anything
• Igniter continuity and glow, then flame sensor signal during a live firing cycle
• Filter and airflow, then the high-limit switch for an overheat trip
• CO and heat exchanger inspection on every gas furnace, with camera footage if there's a concern
• Duct integrity when we're already in the system, so you know if original ductwork is undercutting the furnace

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

Furnace Not Heating in San Leandro: common questions

Nearby and related

Furnace Not Heating near San Leandro: Oakland · Hayward · Castro Valley .

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