5 Common Furnace Problems and How to Fix Them

As winter approaches, your furnace becomes your best friend. It keeps your home warm and comfortable during the cold months. However, like any home appliance, furnaces can develop problems over time. Some issues are minor and easy to fix, while others might require a professional. In this article, we’ll cover 5 common furnace problems and provide practical, actionable steps you can take to fix them or at least troubleshoot before calling in a pro.

1. Furnace Not Turning On

Problem:

Your furnace is unresponsive, and you’re left with a cold house. This is one of the most frustrating issues, especially during freezing temperatures. The furnace might not turn on for several reasons, including issues with the thermostat, power supply, or internal components.

How to Fix It:

1. Check the Thermostat:
   • Make sure the thermostat is set to “heat” mode and is set to a temperature higher than the current room temperature.
   • Replace the batteries if your thermostat is battery-operated.
   • If the thermostat is malfunctioning, try resetting it or adjusting the temperature to see if the furnace responds.
2. Check the Power Supply:
   • Ensure the furnace is plugged in, and check the circuit breaker to make sure it hasn’t been tripped.
   • If the breaker is off, reset it. If it trips again, there may be an electrical issue, and you’ll need to call an electrician.
3. Inspect the Furnace Switch:
   • Look for a power switch near your furnace (usually a small, red switch on the side). Ensure it’s turned on.
4. Inspect the Filter:
   • A clogged air filter can cause your furnace to overheat and shut down. Check the filter, and if it’s dirty, replace it with a clean one.

If none of these solutions work, it may be time to call a technician for a more thorough inspection.

2. Furnace Blowing Cold Air

Problem:

Your furnace is running, but it’s blowing cold air instead of warm air. This could be caused by a few different issues, from a thermostat malfunction to a dirty filter or a problem with the furnace’s ignition system.

How to Fix It:

1. Check the Thermostat Settings:
   • Make sure the thermostat is set to “heat” and not “cool”.
   • If it’s set correctly, try lowering the thermostat by a few degrees and then raising it again to see if that kicks the furnace into action.
2. Inspect the Air Filter:
   • A clogged air filter can restrict airflow, preventing your furnace from heating properly. Change the filter to ensure there’s no obstruction.
3. Check the Pilot Light or Ignition System:
   • If your furnace has a pilot light, ensure it’s on. If the light is out, you can relight it following the instructions in your furnace manual.
   • For modern furnaces with electronic ignitions, listen for a clicking sound. If you hear it but the furnace doesn’t ignite, the ignitor may be faulty and need replacing.
4. Check the Gas Supply:
   • If you have a gas furnace, ensure the gas valve is open. If there’s no gas coming to the furnace, you might need to call your gas provider or a technician.
5. Inspect the Ductwork:
   • Ensure that your air ducts are clear and unobstructed. Blocked ducts or vents can cause poor airflow, leading to cold air being blown.

3. Furnace Making Strange Noises

Problem:

Strange noises from your furnace—such as banging, screeching, or whistling—can be a sign that something is wrong. These noises are often caused by mechanical or airflow issues.

How to Fix It:

1. Banging or Popping Noises:
   • This could be due to delayed ignition or dirty burners. Check the burner assembly for dirt or debris and clean it if necessary.
   • If you hear loud bangs, it could be the sound of air ducts expanding or contracting due to temperature changes. This is normal, but if the sound is constant, it might indicate a bigger issue with airflow.
2. Screeching or Squealing Noises:
   • These sounds are typically caused by a worn-out belt or a malfunctioning blower motor. If it’s a belt, you might be able to replace it yourself, but if it’s the motor, you’ll need a professional to repair or replace it.
3. Rattling or Clicking Sounds:
   • This could be the result of loose parts within the furnace, such as screws or panels. Turn off the furnace and check to see if any parts are loose and tighten them if necessary.

4. Furnace Not Producing Enough Heat

Problem:

Your furnace is running, but it’s not producing enough heat to keep your home comfortable. This could be due to a variety of issues, including airflow problems, dirty filters, or a malfunctioning thermostat.

How to Fix It:

1. Check the Thermostat Settings:
   • If your thermostat is set too low, the furnace won’t produce enough heat. Set it to a higher temperature and wait to see if the furnace adjusts accordingly.
   • Consider replacing an outdated or malfunctioning thermostat if it seems to be giving inaccurate readings.
2. Replace or Clean the Air Filter:
   • A dirty filter restricts airflow, reducing the furnace’s efficiency. Replace the filter with a clean one and make sure your return vents are clear of any debris.
3. Check for Air Duct Blockages:
   • Ensure that air ducts and vents are not blocked by furniture, rugs, or other obstructions. Poor airflow can result in uneven heating throughout the house.
4. Check the Furnace’s Flame Sensor:
   • If the flame sensor is dirty or malfunctioning, the furnace may not produce enough heat. Clean the flame sensor with a soft cloth or replace it if necessary.
5. Look for Leaks in the Ductwork:
   • Leaks or holes in your air ducts can cause warm air to escape before it reaches the rooms of your home. Inspect the ducts for visible leaks and seal them with duct tape or call a professional for repairs.

5. Furnace Turning Off and On Frequently (Short Cycling)

Problem:

Your furnace starts up, runs for a short period, and then shuts off again—only to repeat this cycle. This issue, known as short cycling, can be caused by several different problems, including airflow restrictions or a malfunctioning thermostat.

How to Fix It:

1. Check the Air Filter:
   • A clogged air filter can restrict airflow, causing the furnace to overheat and shut off. Replace the filter if it’s dirty.
2. Inspect the Thermostat:
   • If your thermostat is malfunctioning, it may be causing the furnace to shut off prematurely. Try recalibrating the thermostat or replacing it with a new one.
3. Check the Furnace’s Flame Sensor:
   • A dirty or malfunctioning flame sensor can cause short cycling. Clean the sensor with a soft cloth or replace it if necessary.
4. Check for Blocked Vents or Ducts:
   • Blocked or closed vents can cause air pressure to build up, forcing the furnace to shut off. Ensure that all vents are open and free of obstructions.
5. Inspect the Furnace for Overheating:
   • If the furnace is overheating, it could be due to a dirty burner or blocked flue pipe. Clean these components or call a technician for a thorough inspection

When to Call a Professional

While many common furnace problems can be fixed by homeowners, some issues require professional expertise, such as:

• Gas leaks or electrical issues
• Refrigerant problems (for heat pumps)
• Advanced component repairs, like blower motors or heat exchangers

If you’ve gone through these troubleshooting steps and your furnace is still malfunctioning, it’s time to call in a licensed HVAC technician to inspect and repair the system.

Keeping Your Furnace in Top Condition

Your furnace plays a critical role in maintaining comfort during the cold months. By recognizing common furnace problems early and following these DIY fixes, you can keep your furnace running efficiently throughout the winter. Regular maintenance—such as replacing air filters and cleaning the system—can also help prevent most issues and extend the life of your furnace.

Remember, if you’re ever in doubt or face a more complex problem, don’t hesitate to call a professional to ensure your furnace is working properly and safely. Stay warm and comfortable this winter!