Furnace not heating: what to check, gas and CO safety, and repair cost
For Silicon Valley homes · Updated October 2026 · Sources below
Check the thermostat, the breaker or furnace switch, and the filter first - those cause a lot of no-heat calls. Beyond that, a failed igniter, flame sensor, blower or control board needs a technician. Gas furnaces make carbon monoxide, so a gas smell or a CO alarm means get out first and troubleshoot later.
Smell gas? Leave the house and call 911 and PG&E at 1-800-743-5000 from outside. Don't use matches, lighters, flashlights or light switches. If a carbon monoxide alarm sounds, or people feel dizzy, sick or headachy, get everyone into fresh air and call 911.
The short version
- Check first: thermostat on Heat, breaker and furnace switch on, clean filter
- Smell gas? Leave and call 911 and PG&E at 1-800-743-5000 from outside
- CO alarm sounding? Get everyone out into fresh air and call 911
- California requires CO alarms in homes with gas appliances, a fireplace or an attached garage
- PG&E offers free gas appliance safety checks and pilot relights
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What it costs
- Heating or HVAC repair$130 - $2,000 (average $350)
Typical ranges from published cost guides - mostly national figures. Bay Area prices usually run higher. Your actual price depends on your home and the job, and a pro gives you the real number. Source: HomeAdvisor cost guide (national) (Jun 2026). Have a quote? Check it with the Quote Explainer
Signs you need a technician
- The furnace runs but blows cold air
- It starts and shuts off after a few minutes, or won't start at all
- Banging, screeching or rattling sounds
- A burning or gas smell (gas smell: leave the house first)
- Your CO alarm goes off, or people at home get headaches or feel sick when the heat is on
Repair or replace?
- Usually worth repairing: an igniter, flame sensor, thermostat, blower motor, pressure switch or control board.
- Consider replacing: a cracked heat exchanger, repeated breakdowns, or an old furnace that needs a costly repair.
- If you replace, compare a new furnace with a heat pump - a heat pump also gives you cooling, and local rebates apply when it replaces gas heat.
- A working gas furnace can stay: the Bay Area's 2029 zero-NOx rule applies only to new furnaces sold or installed.
In Silicon Valley
- California's carbon monoxide law (SB 183) requires CO alarms in existing single-family homes that have a fossil fuel heater or appliance, a fireplace or an attached garage. PG&E advises putting them on every floor and near sleeping areas, testing them twice a year, and checking the expiration date - most last five to seven years.
- PG&E offers free in-home gas appliance safety checks and pilot relights for furnaces, water heaters and ovens, especially as the weather cools. You can book them on PG&E's website.
- Bay Area Air District rule: starting in 2029, only zero-NOx furnaces can be sold or installed in the Bay Area. Working furnaces don't have to be replaced, and the Air District has said it may adjust the timeline.
Questions homeowners ask
Why is my furnace not turning on?
Check that the thermostat is set to Heat, set above room temperature and has good batteries, that the breaker and the switch near the furnace are on, and that the furnace door is closed tight. A very dirty filter can also shut it down. If it still won't run, call a technician.
Why is my furnace blowing cold air?
The burners may not be lighting because of a failed igniter, a dirty flame sensor or a gas supply problem, or the furnace may be overheating from a clogged filter and shutting the burners off. Replace the filter, then call a technician if it doesn't come back.
I smell gas near my furnace. What should I do?
Leave the house right away, taking everyone with you. From outside, call 911 and PG&E at 1-800-743-5000. Don't use matches, lighters, flashlights or light switches, and don't go back in until it's declared safe.
What are the signs of carbon monoxide poisoning?
The EPA lists flu-like symptoms without a fever, headaches, dizziness, nausea, weakness, shortness of breath and confusion. If you suspect CO or your alarm sounds, get everyone into fresh air immediately and call 911.
Can PG&E check my furnace for free?
PG&E offers free gas appliance safety checks and pilot relights, which cover furnaces, water heaters and ovens. It's a safety check, not a full tune-up or repair - for a broken furnace, call a heating pro.
How much does furnace repair cost?
National cost guides put heating repair at about $130 to $2,000, with an average around $350. Bay Area prices usually run higher, and parts like a control board or blower motor cost more than an igniter or sensor.
Do I need carbon monoxide detectors in California?
Yes, if your home has a gas furnace or other fuel-burning appliance, a fireplace or an attached garage. Put them on every floor and near bedrooms, test them regularly, and replace them before their expiration date.
Do you need a permit?
Yes - replacing heating or AC equipment needs a permit in California.
General guidance based on California's building code - your city can have stricter rules, and zoning, historic and HOA rules can apply too. Check with your city's building department before you start.
Check the rule for your cityRebates: Heat pump heating & AC
- San José Clean Energy EcoHome Rebates
- Silicon Valley Clean Energy Home Rebates
- Silicon Valley Power Residential Rebates
- City of Palo Alto Utilities Rebate Hub
- Central Coast Community Energy rebates
Rebate programs change often and money runs out. Amounts are from each program's page as of Oct 2026 - always confirm on the program page, and check whether you must apply before you buy or install.
See the rebates for your ZIPQuestions to ask the pro
- What failed, and can you show me?
- Did you check the heat exchanger and for carbon monoxide?
- Is this repair worth it on a furnace this age?
- What would a heat pump cost instead, with local rebates?
- How long are the parts and labor warrantied?
Before you sign, check the contractor's license at cslb.ca.gov. How to hire a contractor in California
Need a heating & AC pro?
Tell us about the job in 2 minutes - free. We send it to one local pro at a time, never a crowd.
Related answers
Sources
- PG&E - Keep yourself safe from a gas leak
- PG&E free gas safety checks and CO tips (news release, Nov 2025)
- U.S. EPA - Carbon monoxide fact sheet
- Menlo Park Fire Protection District - California carbon monoxide alarm law (SB 183)
- Bay Area Air District - Rules 9-4 and 9-6 fact sheet (furnaces and water heaters)
General information for Silicon Valley homeowners, not professional advice for your home. Rules and programs change - check the source, and have a licensed pro look at your situation.