Furnace repair: symptoms, costs, and when to call

Most furnace repair calls come down to a short list of faults: a thermostat or power problem, a clogged filter, an ignition or flame sensor fault, a blower or inducer motor, or a safety switch doing its job. Check the thermostat, breaker, furnace switch and filter first. Anything involving gas, wiring or the burner compartment needs a licensed technician.

Updated November 2026 · General guidance, not an on-site diagnosis

Safety first. If you smell gas (a rotten-egg odor) or a carbon monoxide alarm sounds, leave the house right away and call your gas utility or 911 from outside. Do not flip switches, use a phone indoors, or try to find the leak.

How a gas furnace starts, and where it fails

A gas furnace runs the same sequence every time the thermostat calls for heat. Knowing the order helps you describe the problem to a technician.

The thermostat calls for heat. A dead thermostat, a tripped breaker or a switched-off furnace stops everything here.
The inducer fan starts and pulls air through the burners and out the vent. A pressure switch confirms the vent is clear.
The ignitor heats up or sparks and the gas valve opens. Older furnaces use a standing pilot flame instead.
The flame sensor confirms the burners are lit. If it cannot detect flame, the control board shuts the gas off within seconds.
The blower starts and pushes warm air through the ducts. A limit switch shuts the burners down if the furnace overheats, which usually traces back to restricted airflow.

When a step fails, most furnaces lock out and flash a code on the control board. That code is the fastest clue you have.

What you can check yourself

A few safe checks solve a real share of no-heat calls, and none of them require opening the furnace:

Thermostat set to Heat, set above room temperature, with fresh batteries.
Furnace breaker on, and the wall switch near the furnace on.
Filter clean and installed in the right direction.
Supply registers and return grilles open and uncovered.
On a high-efficiency furnace, the condensate drain line clear and the outdoor vent pipes free of snow, ice or nests.

Stop there. Gas valves, burners, ignitors, wiring and anything behind the burner compartment door belong to a licensed technician.

What drives the repair bill

The cost of a furnace repair depends on four things: the part that failed, how long it takes to reach and replace it, whether the visit is after hours, and whether the part is still under the manufacturer's warranty. Small parts such as ignitors and flame sensors sit at the low end. Blower motors, inducer motors and control boards sit in the middle. A failed heat exchanger is the most expensive repair and often tips the decision toward a new furnace.

The furnace repair cost guide breaks this down by part. If the quote is large and the furnace is old, run the numbers in the repair or replace calculator before you approve the work.

When to call right away

Call a licensed pro without further troubleshooting when you see any of these: a gas smell, a carbon monoxide alarm, soot or scorch marks around the furnace, a burning electrical smell, water pooling near wiring, a breaker that trips again after one reset, or a furnace that locks out repeatedly. These point to faults you cannot diagnose safely from the outside.

Common questions

How do I find furnace repair near me that I can trust?

Look for a contractor who holds the license your state or city requires for heating work, carries insurance, and gives you a written price before starting. Ask what the diagnostic fee covers and whether it is credited toward the repair. A technician who explains the failed part and shows it to you is a good sign.

Is gas furnace repair something I can do myself?

Very little of it. You can safely handle the thermostat, breaker, furnace power switch, filter, vents and condensate drain. Gas piping, the gas valve, burners, ignition parts and internal wiring carry fire, shock and carbon monoxide risks, and many areas require a license for that work.

Is heater repair different from furnace repair?

People use both terms for the same thing. If your home has a gas or electric furnace with ducts, heater repair means furnace repair. If you have a heat pump or a boiler with radiators, the parts and the faults are different, so tell the contractor which system you have when you call.

Should I repair or replace an older furnace?

Repair usually makes sense when the fault is a small part and the furnace has been reliable. Replacement deserves a look when the heat exchanger has failed, when repairs are becoming frequent, or when one quote is a large share of what a new furnace would cost. Ask for both prices in writing.

Sources

CPSC: Carbon Monoxide Information Center

What is it doing?

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Services

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