As the colder weather approaches, many of us are turning on our furnaces for the first time in months, and they are not working. This can be an unpleasant surprise, but it’s entirely avoidable with regular seasonal maintenance. An HVAC system is complex, and like a car, it needs to be checked, cleaned and maintained to work as intended. Heating experts agree that a furnace should be inspected annually before the start of the heating season. But, if the stove isn’t working, it’s essential to avoid the urge to panic; there could be an easy fix, and it may be unnecessary to contact an HVAC technician.

What Type of Furnace Do You Have?

Before we go deeper into this topic, it’s important to understand what type of furnace you have installed in your home. If you’re unsure, check the owner’s manual or documentation that came with the stove or search for the make and model online. This should give you the necessary information to understand how your furnace works fully. Many homes are equipped with a forced-air gas furnace; this is the type of furnace we will cover here. When the gas furnace is not working, there are a number of possible causes, including dirty air filters, low gas supply, a faulty pilot light, improper thermostat settings, and more. This article will look closely at seven common reasons why the furnace may not be working.

1.  The Thermostat Settings

As the “brain” of your HVAC systems, the thermostat is one of the first places to look when something goes wrong. Many people fail to change their settings as they go from one season to the next, so they don’t get the performance they need. For the heating season, the thermostat must be set to “Heat,” and the fan switch should be set to “Auto.” This will ensure that the blower unit engages when you call for heat instead of running continuously, which wastes energy. The latest smart or programmable thermostats have error codes explaining something wrong and the probable causes.

Sometimes, making a simple adjustment may work, or you may need to look at the thermostat instead. The thermostat must be positioned out of direct sunlight to prevent directed heat from giving the unit the wrong temperature information. If the thermostat seems confused, the cause may be a dirty sensor or a failing battery. You can often get the thermostat working properly if you clean the sensor and install a fresh battery. If you’re struggling with an older thermostat, consider an upgrade to a programmable or intelligent model that offers more functionality and features. Many smart thermostats are compatible with older HVAC systems, but that can vary greatly depending on the make and model. If you can’t fix the problem or you want to upgrade your thermostat, contact a professional HVAC technician.

2.  Electrical Supply Interruption

The source of the problem could lie within the gas furnace itself; in some cases, this may be something you can fix yourself. All furnaces, even forced-gas models, require an electrical supply to work correctly. If the power has been turned off accidentally or a breaker has been tripped, the furnace cannot work. Most modern furnaces have a dedicated power disconnect switch next to the stove. Check the breakers, flip them, and restore the power to see if this fixes the problem. If the furnace continues to trip the breaker, it’s time to contact a local HVAC technician to find the root cause of the problem and fix it for you.

3.  Dirty Air Filters

The furnace relies on a supply of air to work efficiently. This air comes through air filters to restrict the flow of airborne contaminants into the sensitive equipment. Over time, the air filters can become clogged with dirt, dust, and other particulates that coat the filter surfaces. Some air filters can be removed, cleaned, and replaced to restore normal operations. Different models may have air filters that must be replaced regularly to ensure that the airflow is maintained.

Most HVAC experts agree that an air filter should be cleaned or changed regularly every 90 days during the heating season. They should be checked before the heating season begins to ensure that the furnace is ready to go when you need it. Checking the air filters is also a standard practice as part of an annual furnace health checkup which is highly recommended. Regularly maintained HVAC systems perform better, use less energy, and are less likely to fail when you need them most. If the air filters have been cleaned or replaced and the problem persists, this may mean that the ducts need to be professionally cleaned.

4.  Gas Supply Issues

This may seem obvious, but if the gas furnace isn’t getting a sufficient supply of gas, it won’t work. The first thing to check is that the gas is turned on because you may have turned it off when the warmer weather arrived. Outside, you should find the gas shut-off valve and it should be fully opened. To check that your home is receiving gas, turn on a different gas-using appliance, such as a stove, if you have one.

If you are receiving gas, it’s likely that the gas line to your home is not the problem. It could be that the gas supply to the furnace itself may be partially or completely closed. There could be insufficient fuel to ignite the gas furnace, and the gas line could have a kink or obstruction. Contact a professional to take a look at the gas line and make a repair or replacement as needed. If you can smell or suspect a gas leak, evacuating the home is essential. Then, a professional will be contacted to evaluate the situation and determine if it is an emergency situation.

5.  A Faulty Ignition Sensor

An ignition sensor is often referred to as a pilot light, and if it’s faulty, the furnace cannot ignite, and no heat can be generated. A common sign that this is the cause of the problem is a furnace click that isn’t followed by firing up. The good news is that a dirty or faulty ignition or sensor is easy to fix without special skills, training, or tools.

To start, turn off the gas in the furnace, remove the front panel, and find the ignition and ignition sensor. This can usually be found in a compartment next to the gas burners. Turn off the power at the breaker box, remove the connected wires, and remove the igniter with a screwdriver. Now you can examine it for signs of damage and evaluate how dirty it is.

Take care if the igniter is fragile; if you handle it roughly during the removable and cleaning process, it may be damaged. The metal part of the sensor should be rubbed gently with a dry, soft scotch brite pad or soft steel wool to remove the gunk.

When the surface looks clean, follow up with a clean paper towel to remove any remaining dust. Then, put the sensor back in place, reconnect the wires, and restore power. Turn the heat at the thermostat and wait to see if the furnace will fire up correctly. If this is the first time that you’ve lit the gas furnace, it may take a few minutes to light.

6.  A Cracked Heat Exchanger

One of the most alarming things about a crack in the heat exchanger is that it may seal back up when the surface is cold. So, it may be impossible to notice unless the furnace is running. If that wasn’t bad enough, the crack could be releasing deadly carbon monoxide (CO) into the home, which is known as “the silent killer” for good reasons.

Multiple house fires are caused by cracked heat exchangers in poorly maintained heating systems every year. There are a few ways to determine if this is a problem in your home, and you must take steps to protect yourself and your family.

First, ensure you have a CO detector near your furnace and on each level of your home. The batteries should be changed regularly, giving you ample warning about a CO leak. Then schedule an annual service for your furnace before the start of each heating season. An HVAC technician will check the heat exchanger and many other components as part of their routine checks. If a heat exchanger is cracked, it cannot be fixed and must be replaced with a new one.

7.  Bad Ductwork

If the ductwork has been improperly fitted or it’s old, cracked, and worn, it will have gaps or holes where the treated air can escape. The ductwork may be blocked with dust and dirt, and cleaning may be required to restore the proper airflow. Leaky air ducts are inefficient; you’re paying for treated air escaping, which is a waste of money. A temporary repair with duct tape is simply a stop-gap fix. When you can, contact your local professional HVAC specialist and ask about ductwork repairs or upgrades.