Furnace Not Working After a Power Outage? Here’s What To Do

Power supply to your building can be cut off for several reasons, the most common being power cable getting cut during construction, storms, and lightning strikes. Power outages are not only inconvenient, but they can also be bad for your furnace. They can cause blown fuses, capacitors, and other problems with electronics.

If your furnace isn’t working after a power outage, you need to test the furnace’s power supply from the breaker box to the main power supply. You should also inspect the furnace’s electronics to determine whether some parts of your furnace need a simple restart, a repair, or a complete replacement.

This article will explain what steps you need to take to determine why your furnace isn’t working after a power outage and how to fix the problem.

Determine the Cause of the Power Outage

As mentioned in the introduction, there are several reasons why a power outage might happen. Depending on what caused it, you may need to call a qualified electric technician to fix electric cables before troubleshooting the furnace. If you notice hanging, cut, or frayed cables in and around your house, please don’t attempt to fix them.

A power outage caused by a lightning strike can blow a fuse in the main electrical panel or the furnace’s circuit breaker. Fuses are easy to fix, and as long as you know the model number, you can replace the fuse with a new one.

In the case of storms, the rain may have caused water damage, and there’s probably a lot of water around your building. Water-damaged furnaces often need a complete replacement, not a repair. 

Assessing the Furnace’s Power Supply

Since your furnace stopped working after a power outage, you need to determine whether all parts are getting power. Here’s what you need to do:

Turn On the Furnace

The furnace has a power button close to it. Check whether you turned it off before the outage and turn it back on. 

Wait a few minutes to see whether the furnace will pick up. If it does, then the issue is solved. If not, keep reading because there are a few other things you can try.

Assess the Breaker Panel

The breaker panel distributes the power from the national grid throughout your house. The board contains several mini-switches that supply power to specific areas of your building. Remember to use safety gloves when dealing with electrical faults. I recommend the DEX FIT Level 5 Gloves (Amazon.com) because of their durability and stretch fit.

You can recognize a problem with the breaker panel if:

• There’s a burning smell coming from the box. 
• The circuit breaker is emitting too much heat.
• There are ragged wires.
• There are switches between ON and OFF.

Circuit breakers are usually labeled; if you can’t locate the furnace breaker, look for tripped switches that supply 15A since most furnaces have a 15A circuit. 

Other electrical issues are too complicated to handle. In the case of a burning smell or ragged wires, switch off the heating system and call a qualified electrician.

Most heating systems have both an indoor and an outdoor circuit breaker. You might find that one works fine, but the other has a tripped circuit. It’s best to test both if the furnace isn’t working correctly.

In the case of a tripped breaker, all you need to do is reset it. The reset process is relatively simple:

1. Turn the furnace’s breaker switch off for 30 seconds to drain off all residual power. 
2. Turn the switch back on. 
3. Switch on the furnace to see if it works.

For Older Furnaces

Furnaces about two decades old have Ground Fault Interrupter (GFI) outlets. These outlets detect electrical faults and can shut off power automatically. GFIs used to be common in furnaces installed in areas prone to water damage, i.e., basements.

Assess whether there’s a trip to the GFI outlet and fix accordingly. For a thorough step-by-step guide on resetting a tripped GFI outlet, watch Lenhart Electric’s video:

Check Your Thermostat

Short power outages may not affect the thermostat. Older thermostats used to be separated from the power, and some had battery control. Nowadays, you can find thermostats inside the furnace, meaning they have the same power supply.

Even though some thermostats can be powered by batteries, they still need electricity to send signals to other heating system components. If the power went out for more than ten minutes, your thermostat could have reset itself back to factory settings. Consult the user manual to set the thermostat to your preferences.

Your thermostat could also be off. Is the thermostat’s display lighting up? If not, restart it. Turn the thermostat on, choose the HEAT setting and automatic fan ON.

Reset Your Thermostat

Here’s how to reset your thermostat if it’s not working correctly:

1. Switch off the thermostat.
2. Switch off the circuit breaker that controls your HVAC system.
3. Wait 30 seconds.
4. Turn it back on.
5. Turn the thermostat on and set your preferred temperature. Be patient; the furnace will take a few minutes to kick in. 

Restart Your Furnace

To restart your furnace, you need to check what model it is. Older models use a standing pilot light to heat the gas entering the furnace’s burners. The pilot valve, which controls the light, is located near the gas burners and is box-shaped:

1. Turn the circuit breaker off for a minute, then turn it on.
2. Switch off the gas control valve.
3. Wait for at least 5 minutes so that the gas retained in the pipe dissipates. This will prevent a fire outbreak in your furnace.
4. Turn on the gas. The flame might go out again if you don’t turn it on quickly. Because pilot valves are hard to reach, I recommend using the Veksun Store’s Electric Lighter (Amazon.com) or Long Reach Matches (Amazon.com) to light the flame up without having to come close to the gas.
5. If you get a flame, confirm that everything is functional and put the access panel back into place.

Shorter Power Outages

Most furnaces need to be reset in case of shorter power outages. The reset process is quite simple. 

Furnaces have a reset button whose location depends on the brand and model. It’ll be red or yellow, and it protrudes when there’s an electrical fault or when the furnace overheats.

Here’s what you do once you find the power reset button:

1. Press the reset button continuously for 30 seconds. This will automatically reset all the settings you programmed. Don’t short-press the controls because you’ll engage the lockdown mode.
2. Turn the thermostat on, choose the HEAT setting, and choose automatic fan ON.
3. Reinstall the access panel.
4. Check whether the furnace is working correctly. Ensure that the safety switch is in place because the furnace won’t turn on without it.

Did You Trigger the Lock Out Mode?

In haste to restart your furnace, you may have engaged the furnace’s lockout mode. Recurring power outages can also trigger this mode. The reset procedure above should clear this problem.

To learn more about the power outage effect on furnaces, watch this funny but useful video by Appliance Princess:

Final Thoughts

Power outages can cause unfortunate circumstances, especially for electrical systems and devices. By staying calm and following this step-by-step guide, you’ll be on your way to a heated home in no time.

You have learned the steps to troubleshoot your heating system after a power outage and what to do. If you can’t fix the furnace, call a qualified professional to help you.

Remember to regularly maintain your heating system so that a minor power outage doesn’t cause any problems.

Vincent Steele

Vincent is a freelance writer based in Santa Ana, California. When he isn’t writing articles for Temperature Master, he can be found biking or hanging out with his cat, Shelly.