Waking up to a freezing home in the dead of winter is a homeowner’s nightmare. If your house feels as cold inside as it is outside, a malfunctioning furnace is likely to blame. A furnace breakdown can disrupt your comfort and safety, making it essential to address the issue promptly.
While any unusual smells like gas or strange noises from your furnace warrant an immediate call to a certified HVAC technician, some furnace problems are minor and can be diagnosed and sometimes resolved by homeowners themselves. This guide provides seven gas furnace troubleshooting steps you can safely perform to diagnose common issues before seeking professional help.
WARNING: Attempting DIY furnace repairs can be dangerous and carry significant health risks. Gas furnaces, if improperly handled, can lead to hazardous gas leaks, exposing your family to toxic fumes and explosion risks. Electric furnaces pose a risk of electric shock during wiring work. Always consult a qualified HVAC professional for any mechanical issues beyond basic troubleshooting.
Gas Furnace Problems Diagnosis Checklist
Before you call for professional furnace repair, walk through this Gas Furnace Problems Diagnosis checklist. These seven steps can help pinpoint the issue and potentially restore heat to your home.
Verify Thermostat Settings for Heat
The simplest solution is often overlooked. Before assuming a major furnace malfunction, ensure your thermostat is correctly set. It’s possible the thermostat is simply turned off, needs new batteries, or was accidentally switched to “cool” or “off.”
First, confirm the thermostat is powered on. If it’s battery-operated, try replacing the batteries. Next, check that the thermostat mode is set to “heat.” Finally, ensure the set temperature is at least five degrees Fahrenheit above the current room temperature. If the thermostat settings are correct, but the furnace still isn’t running, proceed to the next troubleshooting step.
Inspect and Open Air Vents
Your gas furnace generates heat and distributes it throughout your home via a system of air vents. If your furnace is running but your house isn’t warming up, check your vents. Make sure all air vents in each room are fully open and unobstructed.
Vents are typically located on floors, walls, or ceilings. Blocked or closed vents restrict airflow, preventing heat from circulating effectively. Ensure furniture, rugs, or curtains are not blocking any vents. Properly opened vents are crucial for efficient heat distribution throughout your home.
Examine and Replace or Clean the Furnace Filter
A common cause of reduced furnace performance is a clogged or dirty furnace filter. Furnaces, like all HVAC systems, rely on filters to trap dust and debris, keeping the system clean and air quality healthy. Over time, these filters can become clogged, restricting airflow and reducing heating efficiency.
Before inspecting the filter, always turn off your furnace completely for safety. The filter is usually located near the blower, the part of the furnace that forces heated air through your ductwork. The blower’s location depends on your furnace type:
For horizontal furnaces, the blower is typically on the side, and the filter slides into a designated rack.
Alt text: Location of furnace filter in a horizontal gas furnace, showing the slide-in rack access point.
For vertical furnaces, the filter is usually found in the top or bottom door section, depending on whether airflow is upward or downward through the blower.
Alt text: Filter access point in a vertical gas furnace, highlighting the door location for filter inspection.
Once you locate the filter, carefully remove it and inspect for accumulated dust and debris.
Important: Never operate your furnace without a filter. Doing so can lead to significant and costly damage to the system.
If you use disposable filters and it appears heavily soiled, replace it with a new filter of the correct size and type. If you have a reusable filter, wash it with water, let it air dry completely, and then reinstall it. Regular filter changes are essential for maintaining furnace efficiency and air quality.
Power Switch and Breaker Panel Check
If your furnace isn’t heating at all, it might not be receiving power. First, check the furnace’s local power switch, usually located on or near the unit. Ensure it hasn’t been accidentally turned off.
If the furnace switch is on, check your home’s electrical panel. Locate the breaker labeled “furnace” or “heat.” Verify that the breaker is in the “on” position. Try toggling the breaker to the “off” position and then back “on” again. If the breaker trips (switches to “off” immediately or soon after turning the furnace on), this could indicate a more serious electrical issue within the furnace, and you should contact an HVAC professional. Repeatedly resetting a tripped breaker without diagnosing the underlying problem is not recommended.
Observe the Furnace Flame Color
For older gas furnace models with standing pilot lights, the burner flame color is a visual indicator of proper operation. A healthy gas furnace flame should be blue and even.
If you have an older furnace with a visible flame and notice yellow or uneven flames instead of a consistent blue flame, this could signal dirty burners or burner obstructions. Yellow flames often indicate incomplete combustion, which can lead to carbon monoxide production. If you observe yellow or irregular flames, it’s crucial to schedule professional furnace maintenance and burner cleaning promptly. Newer furnaces with electronic ignition systems do not have a constant visible flame.
Pilot Light or Electric Igniter Inspection
Older furnaces use a pilot light – a small, continuous flame – to ignite the main burners. Newer models use an electric igniter, which only activates when heat is needed, eliminating the need for a standing pilot.
If your older furnace has a pilot light that has gone out, you can attempt to relight it. Locate the gas valve knob, usually near the pilot light assembly. Turn the knob to the “off” position, wait for a minute to allow gas to dissipate, and then turn it to the “pilot” setting. Press and hold the reset button while attempting to relight the pilot with a long lighter or match. Once lit, hold the reset button for about a minute before releasing it, ensuring the pilot flame stays lit. If the pilot light repeatedly goes out or you are uncomfortable relighting it, contact an HVAC technician.
For newer furnaces with electric igniters, troubleshooting igniter issues is not a DIY task. If your newer furnace is not igniting, it’s best to call a qualified HVAC professional for diagnosis and repair.
Verify the Gas Valve Position
Your gas furnace has gas valves that control the gas supply. The safety valve supplies gas to the pilot light (if applicable), and the main valve controls gas flow to the burners. Ensure the gas valve, typically located on the gas supply pipe near the furnace, is in the “on” position.
If you suspect a gas leak at any point – indicated by a gas odor – IMMEDIATELY LEAVE YOUR HOME. From a safe location, call 9-1-1 and then contact an HVAC professional. Do not attempt to troubleshoot a suspected gas leak yourself. Gas leaks are serious emergencies requiring professional attention.
More Furnace Troubleshooting Resources
For further gas furnace problems diagnosis and specific troubleshooting guides, refer to these helpful resources:
Furnace Hard Lock Out: Causes and Solutions
Furnace Not Turning On
Furnace Not Blowing Hot Air
Why Does My Furnace Smell Like Burning?
Furnace Short Cycling: What It Is and How to Stop It
Furnace Light Blinking – What It Means
Furnace Blower Not Working
Why Is My Furnace Making a Buzzing Noise?
Furnace Won’t Shut Off
Furnace Keeps Tripping Breaker
Furnace Keeps Leaking Water
