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My Furnace Won’t Ignite: What Should I Do?

Furnace Won't Ignite

You are ready to curl up to enjoy a movie on the couch when you realize that it is still freezing in your home despite turning on your furnace. After some quick investigating, you come to the conclusion that your furnace won’t ignite. Sadly, there is not an easy answer to why this might be happening.

Any of the following problems could be responsible for your furnace not working properly:

  • Clogged filters
  • Loose wiring
  • Low gas supply
  • Malfunctioning thermostat
  • Your pilot light is out
  • The furnace is old or broken

Some of these problems will be easier fixes, while others will require professional help. When your pilot light goes out, your furnace won’t ignite and heat your home. Sometimes, this is the only problem that you need to fix, and things will go back to normal. Other times, the pilot light is still on, but other parts of the furnace could be malfunctioning. Or, it could be that your furnace as a whole may just be broken.

In this post, we’ll look at a variety of common furnace ignition issues, starting with the quickest and easiest fix of them all—clogged filters. If a professional usually changes your filters for you and you’re not quite sure how to take care of this yourself, we’ve got you covered.

Person changing a furnace filter

How To Change Your Furnace Filter

A clogged filter is actually the cause of many furnace problems and could be the reason why cold air is blowing out of your vents when the heat is on. Fortunately, changing an air filter is a relatively quick fix.

Follow these steps:

  1. Turn off power to the furnace. Whenever doing any sort of maintenance with your furnace, this should be your first step.
  2. Locate where your furnace filter is on your system. Most filters are located in the blower motor compartment or right underneath it. If you don’t see your air filter underneath the blower motor compartment, you’ll have to remove the furnace cover to look inside of the blower motor compartment. You can always consult with your furnace’s owner manual which will have diagrams of all the important parts and components.
  3. If you need to run to the store to purchase new filters and you aren’t quite sure which size to get, your current filter will have the correct dimensions on it. Pull the filter out just enough to see the dimensions, snap a quick photo of the type of filter you need, get some filters from the store and head home to finish up the process.
  4. Before removing your existing filter, take note of the airflow arrow on it. You’ll want to slide your new filter in so that the arrow is pointing in the same direction.
  5. Have a garbage bag ready so you can quickly place your old air filter straight into the trash. You don’t want to take that filter that is caked with dust and other debris and risk having this debris fall onto the floor or make a trail to your trash can.
  6. Slide the new filter in, making sure the airflow arrow is pointing the correct way.
  7. Turn your furnace back on.

If a new filter doesn’t fix your problem and your furnace still won’t ignite, you may be wondering: Why is my pilot light not lit?

Why does pilot light go out

Why Does The Pilot Light Go Out?

Pilot lights ignite the furnace and heat the air that circulates throughout the house. Depending on the age of your furnace, your pilot light might be gas or electric. A broken pilot light may just be a one-time fix or point to larger issues within the furnace.

There are a few reasons why a gas or electric pilot light may go out, including:

  • The flame is not burning correctly
  • The thermocouple is broken
  • Dirt or carbon has built up around the pilot light

In some cases, there is no specific reason. In these situations, a draft is usually the culprit.

Flame Not Burning Correctly

The pilot light on a gas furnace is usually blue, but may turn yellow if the flame is not burning correctly. A yellow pilot light may mean that your furnace is leaking carbon monoxide. Because of this, if you see a yellow light, turn off the furnace and immediately contact a trusted air conditioning contractor. If you have a gas furnace, you should consider purchasing a carbon monoxide alarm and putting it in or near your bedrooms to wake you if your family is at risk of CO poisoning.

Broken Thermocouple 

The thermocouple is designed to turn off the flame of your furnace if carbon monoxide is leaking or in the event that the pilot light is ineffective. If the thermocouple is not doing its job, you could be at risk. This is a part that you will have to get replaced if you have an issue before you can continue using your furnace.

Dirt Build Up Around Pilot Light

You may just have to clean the area around the pilot light to get your furnace to ignite again. Be sure to turn off your furnace before you start this process. This area of the furnace is very small and delicate.

If you’ve cleaned up the dirt buildup around your pilot light, you’ll now need to know how to turn your furnace pilot light back on.

How to light a pilot light on a furnace

How To Light A Pilot Light On A Furnace

Luckily, most people can turn on their pilot light themselves. That being said, if you approach your furnace and smell natural gas, put your lighter away and get a professional to examine your system first.

If you don’t smell any gas, look on your furnace for instructions on how to turn on your pilot light, which manufacturers usually add onto labels affixed to your unit. This process is similar to turning a computer off and on again to reset.

That means, to relight a pilot light on a gas furnace, simply turn off the gas valve and wait a few minutes. Then set the valve back to the “pilot” setting to ignite the pilot with a long match or lighter. Wait a few seconds until the flame ignites. Homeowners with an electric furnace will have an even easier job. Simply turn off the furnace, wait a few minutes, turn it back on and locate the ignition button. Hold down the ignition button and wait for the pilot light to come back on.

After you’ve relit the pilot light, stick around for a couple of minutes. The flame should be blue. Remember, a yellow pilot light might indicate that you have a carbon monoxide leak or that the pilot light is not working properly.

If the pilot light doesn’t turn on or it turns off again, you probably have one of the problems mentioned earlier. Do a thorough check of the area around your pilot light. If problems persist, call a professional. An experienced repair person will be able to assess whether or not it’s time to replace the furnace or simply make a few adjustments.

Broken furnace

Other Common Problems With Your Furnace

A lot of furnace problems can be resolved by buying a replacement part. However, you may not even have to go that far. Before calling in for a replacement, check for these potential issues.

The Gas Supply May Be Low

If there is no gas coming into your gas furnace, then your heat source will have nothing to ignite. But you have to know where your gas is coming from in order to take the right steps to assess your gas supply.

Homeowners using propane or LP gas will just have to go out to their gas storage tank and read the gas pressure gauge. If the gauge is below 25, then you will need to contact your gas provider for a refill. If the gauge is over 25, you will need to look for other reasons your furnace is not working properly. Homeowners who are connected to the city gas supply won’t be able to check their gas supply on their own. A professional heating and cooling technician can check the supply for you. In the meantime, look for other signs as to why the furnace won’t ignite.

The Furnace Filter May Be Clogged

Similar to your air conditioning filter, your furnace filters can easily become clogged with dirt and dust. As your furnace tries to move air throughout the house, that dust may be pushed out. If you see a lot of dust around your furnace vents and your home isn’t heating, it might be time to change or clean your furnace filters.

The Thermostat May Be Broken

When you change the settings on your thermostat, your furnace should turn on if there is a discrepancy between your desired temperature and the actual temperature in your home. If your thermostat is broken, or the batteries need to be replaced, however, your furnace will not know that it’s time to ramp up the heat. Try replacing the batteries and see if that works. If not, call in a professional to either recalibrate or replace your thermostat.

At some point when you’ve tried everything and your furnace won’t stay on, you’re probably wondering if your unit is broken.

Do You Have A Broken Furnace?

There are a few other signs that your furnace may be broken or needs to be replaced:

  • Your heating bills go up dramatically
  • It has been 15 to 20 years since the furnace was installed
  • You see burn marks, cracks or a large buildup of dirt around the outside of the furnace
  • You’ve tried everything we’ve already recommended to get your furnace to ignite, and you’re still unsuccessful

Even if you’ve cleaned the furnace, consistently replaced the filters and kept your unit in tip-top shape, it might have reached the end of its service life after 20 years. Check to see when the furnace was installed. If more than 15 years have gone by, you may need to start making some room in your budget for a new furnace.

ABC Can Solve Your Heating And Cooling Woes

Furnaces are complex systems, and trying to work on them without special training and tools can create larger problems and can even lead to injuries and damage to your home. Instead of taking these risks, call on the professionals at ABC Home & Commercial Services. Our licensed specialists are available all day and all night to handle any furnace issue you may be having.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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