Furnace Won't Light? Here Is Why and How to Fix It

When your furnace won’t light, it usually means something in the ignition system isn’t working the way it should. It might be the thermostat, a clogged filter, or a worn-out ignitor. Other times, the problem is more involved and more expensive to fix.

The good news is that many of these issues are easy to diagnose, and a few you can fix yourself in minutes. Below, we walk through how to listen for clues from your furnace, what each common cause looks like, which fixes you can safely handle yourself, and when to call a professional.

Smell Gas? Stop and Leave

If you smell gas near your furnace (a sulfur or rotten egg odor), do not troubleshoot anything. Leave the house right away and call 911 or your gas company from outside. Do not flip switches, light a match, or use your phone indoors. Go back in only when a professional tells you it is safe.

Start by Listening to Your Furnace

Before you open any panels, listen. The sound your furnace makes when it tries to start is the fastest clue to what is wrong.

• Clicking, but no flame. Repeated clicking with no ignition usually points to the ignition system. On most furnaces built in the last 15 years or so, that means a failed igniter. On older models, it can mean the pilot light has gone out.
• Fires up, then shuts off after a few seconds. If the burners light and then quit, the flame sensor is the likely culprit. A dirty or failing sensor cannot confirm the flame is there, so the furnace shuts off the gas as a safety measure. This fix is a job for a technician, not one you should attempt on your own.
• No sound at all. If nothing happens when the thermostat calls for heat, look for a power problem first: the furnace switch, the circuit breaker, or the thermostat itself. If the whole system is unresponsive, see our guide on what to do when your central heating is not working.

Hot Surface Ignitor or Pilot Light? Know Which You Have

Your ignitor is what starts the heating process in your furnace. When your system calls for heat, the ignitor sparks or heats up to light the gas, and the burners take over. If the ignitor doesn’t work, the gas never lights, and your furnace will not produce heat.

The type of ignition system you have depends on the age of your furnace, and it determines whether relighting is an option:

• Hot surface igniter (most furnaces built after about 2010): A small ceramic or metal element that glows orange and lights the gas directly. These are consumable parts that wear out, typically every three to five years. There is no pilot light to relight.
• Standing pilot light (older furnaces): A small flame that stays lit continuously and lights the burners when heat is called for. If the pilot light goes out, you can often relight it by following the instructions printed inside the furnace access panel.

For more information on how gas and electric heating systems differ, see our guide on electric and gas heaters.

What to Do If Your Furnace Isn’t Igniting: 5 Tips

Before you start troubleshooting, take basic safety precautions. Turn off the power at the furnace switch or the breaker and avoid touching any wiring or components you're unfamiliar with.

Reminder: When you smell gas at any point, stop immediately, leave the house, and call your gas company or 911 from outside.

When it’s safe, try these furnace troubleshooting tips to see if you can identify the reason why the furnace won't light.

1. Check the Thermostat

Make sure your thermostat is set to “heat,” and the temperature is set above the current room temperature. If it takes batteries, swap in fresh ones. Switching the fan setting to “on” confirms the thermostat still has power. If the thermostat isn’t sending the proper signal, your furnace will not ignite.

2. Check Your Circuit Breaker

Find the switch labeled “furnace” at your electrical panel. If it is out of position or sitting halfway between on and off, flip it fully off, then back on. A tripped breaker cuts power to the furnace, so it cannot ignite. This also doubles as a system reset, which sometimes clears a minor control board glitch. See our tripped breaker troubleshooting guide for help.

If the breaker keeps tripping after a reset, stop there. That is a sign of a deeper electrical problem, and it is time to call a professional.

3. Replace or Clean the Air Filter

A dirty air filter restricts airflow, which may trigger safety features that shut down your furnace. If it is dusty or clogged, replace it. Regular filter changes help your furnace ignite properly and improve efficiency and airflow throughout your home.

Related: See our Step-by-Step Guide to Replacing an AC Air Filter.

4. Inspect the Igniter

With the power off, remove the access panel and look for the igniter near the burners. It is usually a small ceramic or metal part. If it looks cracked or burnt, or you have noticed it does not glow during startup, it is likely faulty. Igniter replacement involves gas and electrical components, so unless you are experienced and your owner's manual walks you through the replacement process, this is the point to call a technician.

5. Look for Error Codes

Most modern furnaces have small LED codes that blink when there’s a problem. These blinking codes can help diagnose what’s wrong with your system.

Count the number of flashes, check your furnace’s manual, or look up the code on the manufacturer’s site. Each pattern maps to a specific issue, such as ignition failure, a pressure switch problem, or a dirty flame sensor. This step can save you time and give a technician a head start if you need to call one.

When to Call a Professional

Some furnace problems are safe to handle yourself. Others involve gas lines, high-voltage components, or safety sensors that require a licensed technician. Call a pro if:

• You smell gas at any point (leave first, then call from outside your home)
• The breaker trips again after you reset it once
• The furnace fires and then shuts off within seconds, which could mean a flame sensor issue
• The igniter is cracked, burnt, or never glows during startup

Gas supply issues should be handled by a professional. If other gas appliances in your home are working normally, supply is probably not the problem. If none of them are, contact your gas company.

Related: Do home warranties cover gas lines? Read about our gas line coverage. 

When My Furnace Won’t Ignite, Should I Replace It?

You don’t always need to replace the furnace because it won’t ignite. In many cases, a small part like the ignitor may be to blame, and that’s often a straightforward, low-cost fix.

However, replacement might be the better option if your furnace is:

• 15 to 20 years old
• Needing frequent repairs
• No longer heating your home efficiently or evenly

A licensed technician can inspect your system and help you decide whether repair or replacement is the better long-term solution.

Take the Next Step to Protect Your Furnace

A furnace that won’t ignite can make your home uncomfortable fast. But many of the causes are generally easy to spot and fix yourself. If you have a First American home warranty and your furnace has a bigger issue, your heating and furnace coverage can help protect your budget from costly repair or replacement bills.

Get a free quote and see how a home warranty can help keep your home warm and cozy.

FAQs: When the Furnace Won’t Ignite

Why does my furnace click but not ignite?

Repeated clicking with no flame usually points to the ignition system. On furnaces built after roughly 2010, that typically means a failed hot surface igniter, which is a consumable part that wears out every three to five years. On older furnaces with a standing pilot light, clicking can mean the pilot light has gone out. Igniter replacement is generally a job for a licensed technician.

Can I relight my furnace pilot light myself?

Yes. If your furnace has a standing pilot light, you can usually relight it by following the instructions printed on a label inside the furnace access panel. Turn the gas control to “off,” wait at least five minutes for any gas to clear, then follow the steps exactly. Furnaces built after about 2010 have an electronic igniter instead of a pilot light, so there is nothing to relight.

What is a hot surface igniter, and how do I know if it's bad?

A hot surface igniter is a small ceramic or metal element that heats until it glows orange and lights the gas at the burners. It replaced the standing pilot light on most furnaces built after roughly 2010. Signs of a failed igniter include repeated clicking with no flame, no visible orange glow during startup, and a visible crack or burn mark on the element. Igniters are consumable parts that typically last three to five years.

Is a furnace not igniting covered by a home warranty?

First American Home Warranty offers heating and furnace coverage that can cover furnace parts when they break down from normal wear and tear.

When should I call a professional instead of troubleshooting my furnace myself?

Call a licensed technician if you smell gas, if the circuit breaker keeps tripping after a reset, if the furnace fires and then shuts off within seconds, or if the igniter looks cracked or does not glow. Flame sensor cleaning, igniter replacement, gas valve work, and control board diagnostics all involve gas or electrical components and should be left to a professional. Thermostat settings, filter changes, and a single breaker reset are safe for homeowners to handle.

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The contents of this article are provided for general guidance only. First American Home Warranty does not assume any responsibility for losses or damages as a result of using this information.

Please be aware that if you disassemble a covered system or item, it can invalidate your home warranty or manufacturer's warranty.