A furnace that won't light, short-cycles, or blows cold air usually has one of a handful of common faults. This guide covers what those are, what the repair costs, when it becomes a safety issue, and how to hire the right technician.
Furnace repair is the diagnosis and fix of a gas or electric furnace or the heating side of a heat pump air handler. A technician checks the thermostat and safety controls, tests the igniter and flame sensor, inspects the burners and heat exchanger, and measures blower performance to isolate the fault.
Most repairs finish in one visit. A diagnostic or service-call fee (typically $75–$169) covers the visit and troubleshooting and is often credited toward the repair. After-hours no-heat calls in cold weather carry a premium.
Match your symptom on our HVAC problem triage for likely causes and safe first checks.
Dead thermostat batteries, a tripped breaker, a dirty flame sensor, a failed igniter, or a closed gas valve.
The blower runs before the burners are hot, the flame sensor is dirty, or the furnace is locking out after failed ignition.
A clogged filter overheating the limit switch, a bad flame sensor, an oversized furnace, or a failing control board.
Delayed ignition from dirty burners — have this checked promptly; it stresses the heat exchanger.
Tripped breaker, blown door-switch, a failed transformer, or a tripped condensate float switch on a high-efficiency unit.
A possible gas leak — leave the home and call your gas utility from outside before anything else.
Installed ranges including parts and labor, before a diagnostic fee.
| Repair | Typical range |
|---|---|
| Thermostat replacement | $100 – $450 |
| Flame sensor | $80 – $250 |
| Hot-surface igniter | $150 – $400 |
| Limit switch | $150 – $400 |
| Gas valve | $300 – $700 |
| Draft inducer motor | $300 – $700 |
| Blower motor | $300 – $1,100 |
| Control board | $300 – $900 |
| Heat exchanger | $1,500 – $3,500+ (often favors replacement) |
Safe to do yourself: replace the filter, change thermostat batteries, confirm the gas shutoff is open, reset the breaker once, and make sure the furnace door panel is fully seated.
Stop and call a licensed technician immediately for:
If you smell gas or a CO detector sounds, leave the home immediately and call 911 or your gas utility from outside. Do not use switches or open flames.
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Most furnace repairs run $150 to $700 including parts, labor, and a diagnostic fee. Igniters, flame sensors, and limit switches are usually under $400; a blower motor, gas valve, or control board runs higher, and a cracked heat exchanger often costs enough to favor replacement. Use the HVAC Cost Estimator.
The blower is likely running before the burners heat up, or the furnace is failing to stay lit. Common causes are a dirty flame sensor, a failed igniter, or a lockout after repeated failed ignition. Replace the filter and, if it continues, have a technician clean or replace the flame sensor and igniter.
Not always. A cracked heat exchanger, gas leak, or repeated ignition failures can be hazardous. Turn the furnace off and have a licensed technician inspect it if you notice a gas smell, soot, a yellow flame, or a CO alarm.
If the furnace is more than about 15 to 20 years old and the repair is a major component like the heat exchanger or control board, replacement is usually the better value. The Repair or Replace calculator weighs it out.
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