Gas smell or carbon monoxide alarm: do this first
- Rotten-egg smell: Leave the house now. Don't flip light switches, use the thermostat, or start a car in an attached garage. Once you're outside, call 911 or PG&E's gas emergency line at 1-800-743-5000.
- CO alarm sounding: Get everyone outside, pets included, and call 911. Headache, nausea, or dizziness that improves once you're out of the house is a warning sign.
After the utility or fire department clears the house, call us to find the cause before the furnace is used again. California law requires carbon monoxide alarms in homes with gas appliances, fireplaces, or an attached garage, so if yours is missing or more than about 7 years old, replace it.
Signs your furnace needs repair
A furnace needs repair when it blows cold air, won't light, lights and then shuts off, cycles on and off too often, shows a yellow flame, or makes a bang, squeal, or rumble.
- The blower runs but the air is cold. The burners aren't lighting, or they light and shut off. On high-efficiency furnaces, a clogged condensate drain is a common cause.
- Clicking, glowing, or a brief flame, then nothing. If the burners light for a few seconds and then go out, the flame sensor is usually dirty. If the ignitor never glows, it may be cracked.
- The furnace tries 3 or 4 times, then stops. The control board has gone into lockout after repeated failed starts. Look for a blinking LED on the board, visible through the small window in the furnace door.
- A yellow, lazy, or lifting flame instead of a steady blue one. Burners may be dirty, combustion air restricted, or the heat exchanger damaged. Call before using it more.
- A boom or bang at startup. Delayed ignition: gas builds up before it lights. It strains the heat exchanger and should be checked.
- Squealing or rumbling from the blower, or a blower that won't shut off.
- Short cycling. The furnace heats for a minute or 2 and shuts off, often from an overheating limit switch caused by a dirty filter or poor airflow.
- Water around the furnace. Condensing (90%+) furnaces make water and drain it. A leak means a cracked trap, a clogged line, or a failed condensate pump.
A dusty, burning smell for the first hour or 2 of the season is normal: dust burning off the heat exchanger. A smell of hot plastic, burning wire, or one that lingers past the first day is not normal.
Why Santa Rosa furnaces fail on the first cold night
Santa Rosa's heating season is short. Most homes need heat from about November through March, with nights in the 30s and 40s and only occasional freezes. That means the furnace sits unused for 6 or 7 months, and the problems build up while it's idle.
Dust settles on the burners and the flame sensor. Spiders and wasps build nests in burner ports and vent terminals.
In the city's older homes on raised foundations, including many around downtown and in Roseland, the furnace or ductwork is often in the crawlspace, where rats and mice nest in duct insulation and chew control wiring. None of this shows up until the thermostat calls for heat, which is usually the first cold evening, when everyone else's furnace is also being tested.
What to do: run the heat for 15 to 20 minutes in early October. If it lights, runs smoothly, and the smell fades, you're ready.
If it doesn't light, short cycles, or smells wrong, you can book the repair at a calmer time instead of after-hours on a 35-degree night. A fall furnace tune-up catches most of these problems before they cause a no-heat call.
How we diagnose and repair a gas furnace
A gas furnace runs through the same startup sequence every time it starts. Diagnosis means finding the step where it stops:
0Common furnace repairs and the parts that fail
| Part | What it does | What you notice when it fails |
|---|---|---|
| Hot surface ignitor | Glows to light the gas | No glow, no flame, lockout after a few tries |
| Flame sensor | Confirms the burners are lit | Burners light, then shut off within seconds |
| Inducer motor and pressure switch | Clears exhaust and proves the venting is open | Inducer hums but nothing lights; pressure switch fault code |
| Limit switch | Shuts the burners off if the furnace overheats | Short cycling, blower running with no heat |
| Blower motor or capacitor | Moves air through the house | Burners run but no air comes out, or the furnace shuts down on high limit |
| Control board | Runs the sequence | Erratic operation, no response, after a power surge |
| Condensate trap and drain | Removes water from 90%+ furnaces | Water on the floor, pressure switch faults, no heat |
| Thermocouple or pilot assembly | Keeps the pilot lit on older and wall furnaces | Pilot won't stay lit |
What affects furnace repair cost
Furnace repair cost comes down to which part failed, the type of furnace, where it's installed, and whether the call is after hours.
- The part: cleaning a flame sensor or replacing an ignitor is a small job. An inducer motor, control board, gas valve, or variable-speed blower motor costs considerably more.
- Furnace type: high-efficiency condensing furnaces have more parts (condensate traps, PVC venting, 2-stage or modulating valves) than a standard 80% furnace.
- Location: a furnace in an attic or a crawlspace with little clearance takes longer to work on than one in a garage or hall closet.
- Age and parts availability: parts for 20-plus-year-old furnaces and for some wall furnaces can be hard to find.
- Code and safety corrections: a disconnected flue, a missing drip leg, or a vent too close to a window can't be left as is once it's found.
- After-hours timing: a late-night no-heat call can cost more than a daytime visit. Ask about rates when you call.
When you need emergency heating repair
Call immediately for no heat on a cold night when someone in the house is very young, elderly, or ill; for a furnace that keeps running with a burning or electrical smell; or for water leaking from the furnace onto finished floors. Call 911 or PG&E first for any gas smell or CO alarm.
A furnace that simply won't start on a mild night can usually wait for a daytime appointment, and that keeps the cost down. Our emergency HVAC repair page explains how to tell the difference.
Repair or replace an old furnace?
A cracked heat exchanger on an older furnace usually means replacement, because the repair costs close to as much as a new furnace. A furnace past about 20 years old that needs a major part is also worth comparing against furnace replacement.
With Santa Rosa's mild winters, a heat pump is a strong alternative to another gas furnace, especially if the air conditioner is due for replacement too. For homes heated by a single wall furnace, a ductless mini-split adds cooling and spreads heat more evenly.
Furnace work is a core part of the HVAC service in Santa Rosa that HVAC Pros provides, along with the AC, ductwork, and filtration that share the same blower.
What to watch after furnace repair
Put in a fresh filter and check it monthly through winter. Watch the first few heating cycles: the burners should light within a few seconds of the inducer starting and stay lit until the thermostat is satisfied.
Test your CO alarms monthly. If the same fault code comes back, note when it happens (first start of the morning, after a long run, during wind or rain) and tell the technician, because the pattern helps pin it down.
Furnace repair questions from Santa Rosa homeowners
Why does my furnace smell like burning the first time I turn it on?
Dust collects on the heat exchanger and burners over the summer and burns off the first time the furnace runs. The smell should fade within an hour or 2. If it smells like burning plastic or wiring, or it doesn't fade, turn the furnace off and call.
My furnace lights, then shuts off after a few seconds. What's wrong?
Most often it's a dirty flame sensor. The furnace can't confirm the flame, so it shuts the gas off as a safety measure.
Cleaning it is a quick repair. Poor grounding, a bad sensor, or weak gas pressure can cause the same symptom, and a technician can measure which one it is.
Is it safe to run a furnace with a cracked heat exchanger?
No. A crack can let combustion gases, including carbon monoxide, into the air going through your home. If a technician finds a crack, the furnace should be shut off and the gas valve turned off until it is replaced.
Do you repair wall furnaces and floor furnaces?
Yes. Wall and floor furnaces are still common in older Santa Rosa homes, and pilot outages, thermocouples, dirty burners, and venting problems are often repairable.
Because these units heat a small area right next to living space, we also check clearances to furniture and curtains and the condition of the vent. If the unit is very old or parts aren't available, we'll explain replacement options.
How often should a gas furnace be serviced?
Once a year, ideally in September or October before you need it. A tune-up covers burner and flame sensor cleaning, ignitor and safety switch checks, venting inspection, gas pressure, and a combustion and CO check.
No heat? Get furnace repair in Santa Rosa
Tell us what the furnace is doing (no glow, a flame that drops out, a blinking code, cold air) and we'll send a technician to find the cause. We take calls 24/7 at (707) 283-3186.