Bay Area winters are mild compared to most of the country, and that's exactly what gets furnaces into trouble. A system that sits idle for eight or nine months, then gets asked to run hard the first genuinely cold night of the season, is the classic setup for a no-heat call. Every year the pattern repeats: the first real cold snap hits — usually in October or November — and the phones start ringing with furnaces that won't light or aren't heating. A lot of those calls are preventable.
None of the checks below take more than a few minutes, and most cost nothing. Work through this list before the first cold night, not during it, and you'll either catch a small problem while it's still cheap and easy to fix, or head into winter knowing the furnace is ready.
Your pre-season furnace checklist
- Replace or check the air filter. A dirty filter is the single most common cause of furnace trouble — it chokes airflow and can trip a safety switch that shuts the burners down. If you can't remember the last time it was changed, change it now.
- Clear vents and returns of furniture and clutter. A rug, a bed frame, or a stack of boxes in front of a supply vent or return grille blocks airflow the same way a dirty filter does. Walk the house and make sure every vent and return can breathe.
- Test the thermostat before the cold snap actually hits. Switch it to HEAT, bump the setpoint a few degrees above room temperature, and confirm the furnace responds. Replace the batteries if it takes them, and double-check any schedule or setback programming still makes sense for the season.
- Expect a brief "dust burn-off" smell on the first run — but not a lingering one. A faint, dusty smell for the first few minutes after the furnace's first fire of the season is normal; it's dust burning off the heat exchanger. A smell that lingers, gets stronger, or smells electrical or like burning plastic is not normal — shut the furnace off and have it checked.
- Check the pilot light or ignition on older units. If you have an older standing-pilot furnace or wall heater, confirm the pilot lights and stays lit — newer furnaces use electronic ignition instead.
- Clear debris from outdoor vent and intake terminations. High-efficiency furnaces vent through a wall or roof termination that can get blocked by leaves or wind-blown debris. A blocked vent is a safety issue, not just a performance one — clear the area around it.
- Consider a professional tune-up before the first cold snap. A tune-up covers what you can't easily check yourself: cleaning the flame sensor, testing safety switches, and running a carbon monoxide check on the heat exchanger. Booking it in September or early October also means you're not competing with everyone else's emergency no-heat call for the next available appointment.
Why fall furnace prep matters in the Bay Area
A furnace that runs only a few months a year is different from one that runs most of the year — the idle months are when dust settles on components, and igniters and flame sensors sit unused long enough that the first real cycle of the season is often the one that exposes a part already on its way out. That's why "first cold snap" and "no-heat call" go together so reliably in our service area.
It also matters because a lot of Peninsula and East Bay homes still run older furnaces, and age plus disuse is a rougher combination than age alone. If a part has genuinely failed, the common fixes aren't dramatic: a hot-surface igniter runs about $120–$350 and a flame sensor about $90–$250, while a control board is a less common repair at roughly $200–$600. A tune-up costs far less than any of those — the whole case for doing it before something breaks rather than after.
Carbon monoxide safety is the other reason this is worth taking seriously. A cracked heat exchanger or a venting problem isn't something you can see or smell reliably, which is exactly why the CO check is part of a real tune-up and not something a DIY look can fully substitute.
Get ahead of the rush
The best time to deal with a furnace problem is before it's 45 degrees at 6 a.m. and every other homeowner is calling for the same reason. Triton services gas and electric furnaces across the Peninsula and East Bay as part of our full HVAC repair service — San Mateo, Burlingame, Redwood City, Alameda, San Leandro, and Hayward. Licensed techs, upfront pricing, and a diagnostic fee credited toward the repair when you approve the work.
Book online or call (888) 993-5699. Get the furnace checked now, while it's still easy to get on the schedule.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Furnace Not Heating / No Heat — what to do once it's already failed
- Furnace Won't Ignite (Clicks, No Flame or No Start) — the most common first-cold-snap failure
- Pilot Light Won't Stay Lit (Furnace or Wall Heater) — older standing-pilot units
- Furnace Repair Cost Guide — typical part-by-part pricing
- HVAC & Furnace Repair in San Mateo — Peninsula service area
Frequently asked questions
When should I get my furnace serviced before winter? Aim for September or early October, before the first real cold snap. Booking early means you get a routine appointment instead of competing with everyone else's emergency no-heat call once the weather actually turns, and it gives a tech time to fix anything found before you actually need the heat.
Why does my furnace smell like it's burning when I first turn it on? A faint dusty smell for the first several minutes of the season's first run is normal — it's dust that settled on the heat exchanger over the summer, burning off. It should fade quickly. A smell that lingers, gets stronger, or smells electrical or like hot plastic is not normal; shut the furnace off and have it looked at.
Do I really need a professional tune-up every year? It's not mandatory, but it's the only way to check things like the flame sensor, safety switches, and a carbon monoxide reading on the heat exchanger, which aren't practical DIY checks. It also tends to be far cheaper than the repair — or the emergency call — that catches a worn part after it fails instead of before.
What size air filter does my furnace need, and how often should I change it? That depends on the furnace and the filter type printed on the old filter's frame, so check there or in the furnace manual rather than guessing. As a general rule, a basic filter should be checked monthly and changed roughly every 1–3 months, more often if you have pets or run the fan constantly.
Is a pilot light that keeps going out something I can fix myself? Relighting it once, following the instructions on the furnace panel, is fine. If it won't stay lit or keeps going out repeatedly, that usually points to a worn thermocouple or a draft issue, and it needs a tech rather than repeated relighting.
What if my furnace still won't heat after I've gone through this checklist? That points to something beyond a simple seasonal check — most likely a failed igniter, a dirty flame sensor, or a gas or ignition fault. Our furnace not heating guide walks through the common causes, or call us directly and we'll send a tech to diagnose it.