What to Do If Your Furnace Isn’t Heating After a Power Outage in St. Louis

If your furnace isn’t heating after a power outage, follow these quick checks:

• Verify the furnace has power at the breaker box and wall switch
• Make sure your thermostat is on “Heat,” set above room temperature, and has working batteries
• Reset the furnace by turning off its switch for a minute, then back on
• Inspect the pilot light or ignition system to ensure it’s lit
• Check and replace a dirty air filter; clear vents and registers
• If it still won’t heat, contact a qualified HVAC technician

These steps resolve most post-outage issues.

 

Check the Power at the Furnace

 

When electricity goes out, a hidden switch or breaker can stay off even after power returns. In your home’s breaker panel, look for the switch labeled “Furnace,” “HVAC,” or “Air Handler” and flip it fully off and then on again. Nearby the furnace itself you’ll often find a red or yellow wall switch—make sure it’s in the ON position. If your furnace uses a fuse instead of a breaker, check the fuse housing for a blown fuse and replace it with one of the same size and type.

 

Verify Thermostat Settings and Power

 

Your thermostat controls when the furnace turns on. After a power outage some thermostats reset to “Off” or lose programming. To fix that:

• Set the mode to “Heat” (not “Cool” or “Off”).
• Raise the temperature setting several degrees above the current room temperature so the furnace starts.
• If the display is blank, replace its batteries (usually AA or AAA) or check its circuit fuse.
• For smart or programmable thermostats, follow the manufacturer’s instructions to restore Wi-Fi connections if needed.

 

Reset the Furnace and Safety Switches

 

Most modern furnaces have a safety reset button or switch on the main unit. To reset:

• Turn off the furnace at the wall switch or breaker.
• Wait 30–60 seconds to let internal circuits discharge.
• Press the red reset button (if present) once, then restore power.

This can clear any internal safety lockouts caused by voltage drops during the outage.

 

Inspect the Pilot Light or Electronic Ignition

 

Older furnaces use a small pilot flame that must stay lit to ignite the main burner. If it went out:

• Open the furnace door and look for a small flame in a glass or metal tube.
• If it’s out, consult the furnace label for lighting instructions—usually holding a match or using the built-in igniter button.

Newer furnaces use an electronic ignition system rather than a pilot light. You may hear clicking or see a glow. If there’s no light or sound, the ignition control module or flame sensor might need cleaning or replacement, which is a job for a technician.

 

Check and Replace the Air Filter

 

A dirty filter restricts airflow and can make the furnace overheat and shut off. Locate the filter in a slot near the blower or air return vent. If it’s dark with dust or pet hair, replace it with the correct size filter rated MERV 6–8 for homes. A clean filter helps heat circulate properly.

 

Ensure Vents and Registers Are Open

 

Blocked vents prevent warm air from moving through your rooms. Walk through your house and gently push open or remove anything covering floor, wall, or ceiling registers. Make sure furniture, curtains, or rugs aren’t blocking them.

 

Know When to Call a Professional

 

If you’ve tried all the above and your furnace still won’t heat, you could have a failed component like a gas valve, limit switch, or control board. Fixing these safely requires training and special tools. Local heating experts like those at Hoffman Brothers—serving St. Louis and Nashville—can diagnose, repair, or replace parts quickly, restoring reliable heat without guesswork.

With these clear steps and explanations, you’ll know exactly what to do when your furnace stops heating after a power outage—and when it’s time to bring in professional help.