Furnace Repair Guide

Furnaces are long-lived but have common failure points. The igniter, flame sensor, and blower motor capacitor are the big three — all under $50 each. Warning: gas furnaces can produce carbon monoxide. If you smell gas, leave the house and call the gas company.

Avg Lifespan

15-20 years

Replace Cost

$2,500-6,000

Common Fixes

3 problems

Common Problems

85% likely easy 15-20 minutes

Not Igniting

Thermostat calls for heat but furnace doesn't fire up

Cause: Dirty flame sensor or failed hot surface igniter

Parts from

$25

See Fix →

55% likely easy 10-15 minutes

Blower Running Constantly

Fan runs non-stop even when thermostat is off

Cause: Thermostat fan setting on 'ON' or stuck fan relay

Parts from

$40

See Fix →

60% likely easy 15-20 minutes

Short Cycling (Turns On and Off Quickly)

Furnace fires up but shuts off within a few minutes

Cause: Dirty air filter, overheating, or faulty high-limit switch

Parts from

$15

See Fix →

Is It Worth Fixing?

A furnace replacement costs $2,500-6,000. Most common repairs cost $10-50 in parts. If your unit is less than 15-20 years old, repairing it is almost always the better financial decision. Even if you're not comfortable with DIY repairs, a service call ($100-200) plus parts is still cheaper than replacing the entire unit.

When to replace: If the unit is past its expected lifespan, has had multiple failures, or the compressor/motor needs replacing (these are expensive components that signal end-of-life).

Brands We Cover

CarrierLennoxTraneGoodmanRheem

Related Appliances

❄️

Air Conditioner

3 fixes

Frequently Asked Questions

How long does a furnace typically last?

A typical furnace lasts 15-20 years. With regular maintenance, many last even longer. If yours is approaching the end of its expected lifespan and a major component fails (compressor, motor), replacement may be more cost-effective.

Is it worth repairing a furnace or should I replace it?

If the repair costs less than 50% of a new furnace ($2,500-6,000) and the unit is under 75% of its expected lifespan (15-20 years), repair is usually the better choice. Most common furnace repairs cost $10-50 in parts.

Can I fix a furnace myself?

3 of 3 common furnace problems are rated "easy" and can be fixed by most homeowners with basic tools (screwdriver, multimeter). Always disconnect power before starting any repair.

What tools do I need to repair a furnace?

Most furnace repairs require a multi-bit screwdriver, adjustable wrench, and multimeter. Total tool investment: under $50. We list the specific tools needed for each repair in our guides.