Gas Furnace Repair: Costs, Common Issues & When to Call a Pro

Gas furnaces account for roughly 45% of residential heating systems in the US, making them the most common furnace type. They're generally reliable, but several components are prone to failure — especially without regular maintenance. For a broader overview of repair costs across all furnace types, see our furnace repair cost guide.

Ignition Problems ($150–$400)

Modern gas furnaces use either a hot surface ignitor or an electronic spark ignitor. These components wear out over time and are one of the most frequent repair calls. Signs of ignition failure include the furnace clicking but not lighting, or the blower running without producing heat.

Older gas furnaces with standing pilot lights can develop thermocouple issues ($100–$300), where the safety device that detects the pilot flame fails and shuts the gas valve.

Gas Valve Failure ($200–$1,500)

The gas valve controls fuel flow to the burners. When it fails, the furnace won't ignite at all. Gas valve replacement is a moderate-to-major repair because the part itself costs $150–$700 and requires careful calibration after installation.

If you smell gas near your furnace, do not attempt any diagnosis. Leave your home and call your gas company immediately. If you need help outside business hours, see our guide to emergency furnace repair.

Flame Sensor Issues ($75–$300)

A dirty or failing flame sensor is the single most common gas furnace repair. The flame sensor is a small rod that detects whether the burners are lit. When it's coated with carbon buildup, it can't sense the flame and shuts the furnace down as a safety measure. Cleaning costs $75–$150; replacement runs $150–$300.

Heat Exchanger Cracks ($500–$3,500)

The heat exchanger is the most critical — and expensive — gas furnace component. It separates combustion gases from your home's air supply. A cracked heat exchanger can leak carbon monoxide, making it a serious safety hazard.

Signs of a cracked heat exchanger:

• Yellow or flickering burner flames (should be steady blue)
• Soot around the furnace
• Strong, unusual odors when the furnace runs
• Carbon monoxide detector alarms
• Visible cracks or corrosion on the heat exchanger

For furnaces over 15 years old, a cracked heat exchanger almost always means replacement is the better option, since the repair cost approaches 50% or more of a new furnace.

Blower Motor Failure ($300–$2,500)

The blower motor circulates heated air through your ductwork. Symptoms of failure include weak airflow, unusual humming or squealing noises, and the furnace overheating. Variable-speed blower motors are significantly more expensive to replace than single-speed models.

A well-maintained gas furnace typically lasts 15 to 20 years. After 15 years, repair frequency increases and efficiency declines.

Signs Your Gas Furnace Is Nearing End of Life

• Frequent repairs — Two or more repairs per heating season
• Rising energy bills — Efficiency drops as components wear
• Uneven heating — Some rooms are warm while others stay cold
• Yellow burner flames — Should be blue; yellow indicates incomplete combustion
• Excessive noise — Banging, rattling, or squealing that wasn't present before
• Carbon monoxide concerns — Older heat exchangers are more prone to cracking

Replacement Cost

A new gas furnace installed costs $3,800–$12,000 depending on efficiency rating:

Important: Federal regulations taking effect in 2028 will require a minimum 95% AFUE for new gas furnaces in northern states. If you're replacing now, choosing a 95%+ AFUE model ensures compliance and maximizes energy savings.