A homeowner off Castledown Road in Pleasanton called about a Carrier gas furnace that would not start cleanly. Some cycles it caught. Other cycles it sat there and did nothing, and when it did fire it ran rough. They had owned the house ten years and told me straight that the furnace had never once been serviced in that time. That is a long stretch to skip. It is not rare, though, and I had a fair idea what I would find before I opened the cabinet.
Two faults had stacked on top of each other
The first was the ignition assembly. The contacts that handle ignition timing had rusted enough that the spark no longer fired reliably, which explains the random misses where one cycle lights and the next does nothing.
The second sat in the exhaust. A decade of dust and an old insect nest had narrowed the flue and choked the draft. A furnace needs a certain amount of draft before it will let the burners run, so on the cycles where draft fell short, the pressure switch tripped and blocked ignition. Either fault by itself would have produced the no-start the homeowner described. With both present at once, a clean light was almost impossible.
The work and the part that matters
I swapped the rusted ignition component for a genuine Carrier part. This is not a spot to drop in a generic, because the ignition timing is specific to the model, and getting it wrong puts you back here within a month. Then I cleared and serviced the exhaust vent end to end so the flue ran clean.
From there I worked through the rest of the system instead of stopping at the two known faults. Burner assembly, heat exchanger, blower, safety controls, all of it got eyes on, because a furnace that has gone ten years untouched rarely has just one thing aging.
Why I ran it through several full cycles
Verification is what made this repair hold. A furnace that lights once for the tech proves nothing. I watched the draft, the pressure switch action, and the full ignition sequence across several complete heat cycles, cold start included, until I was satisfied the new part and the cleared flue were holding under real conditions. That is the gap between a furnace that lights for me and a furnace that lights for the family at 6 AM in January.
Here is the rule I use on the maintenance question, since the homeowner asked. A ten-year gap on a modern gas furnace is not a death sentence. Most will tolerate it. What it changes is what a small repair can do for you. Caught at an annual tune-up, a rusted contact gets cleaned and a flue gets cleared as routine work. Caught at year ten with the furnace down, both get diagnosed cold while you pay repair rates instead of maintenance rates. Our HVAC maintenance plan exists to keep these two failures from ever meeting.
Result
The Carrier is back to reliable startup and clean operation. Draft is restored, ignition timing is back to spec, and every safety control has been checked. The repair carries our 1-year parts and 1-year labor warranty. We waived the $75 diagnostic because the homeowner went ahead with the repair, and they had a written, itemized quote before I touched a thing. If your furnace is missing starts or short-cycling, that is what furnace repair through our HVAC division looks like.
