Furnace Not Heating in Union City, CA

Furnace Not Heating in Union City

Union City is mostly 1970s through 90s tract housing across Decoto and the central neighborhoods, and a large share of those furnaces are on their original or first replacement equipment. Past the 20-year mark, the parts that fail first on a no-heat call are predictable. Hot surface ignitors crack from thermal cycling. Flame sensors carbon over. Gas valves get tired and stick. Winters here are mild, so the furnace does light work most of the year, then a marginal part lets go the first genuinely cold week.

Because the equipment is old, more than one thing can be worn at once. But the no-heat condition itself usually traces to one failed component. The job is to find that part and confirm it, not to assume the whole system is finished. We have put ignitors and sensors into 25-year-old furnaces that then ran fine for several more seasons.

On the oldest units the estimate is where we lay out the real options. If a furnace this age has a cracked heat exchanger or a burned control board, repair stops making financial sense, and a heat pump conversion may pencil out depending on what incentives are open at the time. We show you the failure on the unit and put the numbers in writing before you decide.

Common causes

Cracked hot surface ignitor. On 20-plus-year furnaces this is the number one no-heat cause. The ignitor cracks from thermal cycling and stops reaching light-off temperature. We test it on a meter and watch the sequence, then quote the correct ignitor for your model in writing.

Carboned flame sensor. The furnace lights then drops out within a few seconds because the board cannot prove flame. On aging Union City units this is routine. Cleaning the sensor often fixes it; a pitted rod gets replaced.

Worn gas valve. After two decades of cycling, gas valves can stick or fail to open. If the ignitor heats correctly but no gas arrives at the burners, we check the valve coil and the signal feeding it before condemning it, since a control fault can mimic a bad valve.

Limit switch tripped by a clogged filter. A neglected filter chokes airflow, the heat exchanger overheats, and the high-limit shuts the burners down. Very common in older homes where filters go unchanged. We restore airflow, verify the limit resets, and find the restriction so it does not lock out again.

Failed blower motor or capacitor. Furnace lights but no warm air moves, then it locks out on the trapped heat. The blower motor or its run capacitor is the usual culprit on aging equipment. We test both under load and replace the failed part.

Control board failure. Older boards can lose the ability to sequence ignition, leaving you with a dead-feeling but otherwise sound furnace. We meter the board's outputs and inputs to confirm before quoting, because a board on a 25-year unit is where the repair-versus-replace conversation often starts.

How we diagnose it

Run the ignition sequence and pinpoint where it stops: ignitor not heating, no flame proof, or no gas at the burners.
Meter the ignitor, flame sensor, gas valve, blower capacitor, and control board signals to isolate the failed part.
Inspect the filter and return airflow, the usual cause of a tripped limit on older tract homes.
CO test and visually inspect the heat exchanger, which matters more on furnaces past 18 years.
On the oldest units, document any major failure so the repair-versus-replace and heat pump numbers go on the estimate.

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

Furnace Not Heating in Union City: common questions

Do you cover Union City and how quickly can you come out?

Yes. We run out of San Ramon and serve the inner East Bay including Union City, Fremont, Newark, and Hayward. Same-day is best effort rather than a promise, but no-heat calls get priority and we will give you an honest arrival window when you call (925) 999-4095.

My furnace is over 20 years old. Should I repair it or replace it?

It depends on what failed. A cracked ignitor or dirty flame sensor on an otherwise sound 20-year furnace is worth fixing. A cracked heat exchanger or burned control board usually is not. When you are replacing, a heat pump conversion can shift the math even after the higher equipment cost. We check which incentives are actually open and funded at the time and put the real numbers on the written estimate.

The furnace clicks and tries to start but never lights. What is wrong?

That clicking is usually the ignition sequence beginning and then failing. On older furnaces it most often means a cracked hot surface ignitor that no longer reaches light-off temperature, or a gas valve not opening. We watch the full sequence on a meter to tell which it is rather than swapping parts on a guess.

Nearby and related

Furnace Not Heating near Union City: Fremont · Newark · Hayward .

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