Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
Most furnace repairs come down to a short list of parts: the igniter, the flame sensor, the pressure switch, the blower motor and its capacitor, the limit switch and the control board. A cracked heat exchanger is the one failure that ends the furnace rather than starting a repair.
No federal source publishes what any of these repairs cost, so every price range you find online is a vendor survey. What is documented is the safety side: CPSC estimates 76 deaths from carbon monoxide involving heating systems in 2022.
What actually fails, by symptom
Furnaces mostly fail in one of four ways, and each points at a different group of parts.
| Symptom | Usual suspects | Owner fixable |
|---|---|---|
| No heat, no ignition attempt | Thermostat, power, door switch, control board | Check thermostat and breaker only |
| Ignites then shuts down within seconds | Flame sensor, dirty burners, flue blockage | No |
| Blower runs, air is cold | Igniter, gas valve, pressure switch, limit switch | No |
| Short cycling | Dirty filter, closed vents, oversized furnace, limit switch | Filter and vents, yes |
| Noise on start or run | Blower motor, bearings, capacitor, inducer motor | No |
| Soot, burning smell, alarm sounding | Combustion problem or heat exchanger | Shut it off and call |
The single most common no-heat pattern is a furnace refusing to light because a safety interlock has not proved. Our page on why a furnace will not ignite walks the start sequence step by step.
The parts that fail most
These are wear items on a gas furnace. Each is cheap relative to the machine, and each stops the furnace completely.
- Hot surface igniter. A brittle ceramic element that glows to light the burners. It fails from age and from being touched.
- Flame sensor. A metal rod that proves a flame is present. It gets coated and stops conducting, so the furnace lights and immediately shuts down.
- Pressure switch. Confirms the inducer is drawing properly. A blocked flue or a cracked hose will keep it open, and the furnace will not fire.
- Capacitor. Starts and runs the blower motor. See what a capacitor does.
- Blower motor. Moves the heated air. See blower motor symptoms and types.
- Limit switch. Shuts the furnace down when it overheats, usually because airflow is restricted. A limit switch that trips repeatedly is reporting an airflow problem, not causing one.
A cracked heat exchanger lets combustion gases mix with the air you breathe. It is not repaired; the furnace is replaced or the exchanger is swapped if still under warranty. CPSC estimated 274 non-fire carbon monoxide deaths from consumer products in 2022, of which 76 (28%) involved heating systems, the second largest category after engine-driven tools. CPSC advises “a yearly professional inspection of all fuel-burning home heating systems, including furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents.”
Repair or replace
Three things decide it, and age alone is not one of them.
- What failed. An igniter or a capacitor is a routine repair. A heat exchanger, a control board on an old furnace, or a second major failure in a season pushes towards replacement.
- What the furnace is. An 80% AFUE furnace replaced today can be a condensing model; from December 18, 2028 new non-weatherized gas furnaces must be 95% AFUE, which changes venting. See the 2028 standard.
- Whether it is still safe. Combustion faults are not a cost question.
Age is a weak signal on its own: 20.0% of US homes that heat are running main heating equipment 20 years old or more, and most of it works.
What a furnace repair costs
No federal series measures HVAC repair prices. BLS publishes producer prices for equipment and wages for the trade, but nothing that tells you what a flame sensor replacement costs in your town.
What you can do is make quotes comparable: ask for the part and the labour separately, ask what failed and why, and ask what the technician measured. A part that fails twice in two seasons is a symptom of something else. Our page on what HVAC repair costs are actually measured explains the gap.
How much furnace repair there is to do
The installed base is large and old. A central warm-air furnace is the main heating equipment in 74.42 million US homes, 63.2% of homes that heat, and gas furnace shipments are running below last year, which means more of that base is being repaired rather than replaced.
Frequently asked questions
What is the most common furnace repair?
Ignition-related parts: the hot surface igniter and the flame sensor. Both stop the furnace from producing heat, both are inexpensive parts, and both are routine replacements. Blower capacitors and pressure switches are the next most common.
Is it worth repairing a furnace?
Usually, unless the heat exchanger has failed, the same major component has failed twice, or a combustion fault has been found. What failed matters more than the furnace’s age. A furnace replaced now can also be affected by the 95% AFUE standard that applies to units manufactured from December 18, 2028.
How much does furnace repair cost?
No federal source measures it, so any published range is a vendor survey or contractor estimate rather than measured data. Ask for the part and labour separately, and ask what was measured to reach the diagnosis.
Is a furnace problem dangerous?
It can be. CPSC estimated 76 non-fire carbon monoxide deaths involving heating systems in 2022, 28% of the 274 consumer product CO deaths that year. If a CO alarm sounds, or you smell burning or see soot, shut the system off and get out before calling anyone.
Methodology and limitations
Component descriptions are general to residential gas furnaces. Carbon monoxide figures are CPSC 2022 annual estimates, published May 2026. Installed base is EIA RECS 2020 table HC6.1.
- We publish no repair prices, because no federal series measures them.
- CPSC estimates are for consumer products under its jurisdiction and are revised in later reports.
- Nothing here is a substitute for a qualified technician inspecting your equipment.
Sources
- US Consumer Product Safety Commission, Home Heating Equipment and Non-Fire Carbon Monoxide Deaths Associated with the Use of Consumer Products, 2022 Annual Estimates (May 2026).
- US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.
- Code of Federal Regulations, 10 CFR 430.32(e), furnace efficiency standards.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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