11 Common Furnace Problems

January 12, 2024

We hate when a defective furnace causes indoor temperatures to plummet drastically. When something goes wrong with your furnace, it’s easy to despair and reach for a blanket to stay warm.

Fortunately, the pros at Blue Flame Heating, Air, & Electric have your back! Our HVAC and furnace technicians are standing by, ready for a repair service if you need one. Let’s dive into furnace complications you should know about, and talk through the next steps as outlined by the experts, should you encounter these issues.

Table of Contents

11 Common Furnace Problems

1. Broken Thermostat

When a thermostat malfunctions, the blower fan can run continuously when it doesn’t have to. Or, a thermostat malfunction could damage the electrical system, causing it to register an incorrect indoor temperature, meaning you’ll receive too much or too little heat.

Next step: First, check the settings on the thermostat and see if they’re set to ‘auto.’ This way, the furnace will run when it has to. If that’s not the problem, your thermostat issue may require technical expertise. If so, it’s best to consult an HVAC technician for a repair.

2. Dirty Ductwork

Ductwork can clog with dust and debris. The contaminant buildup restricts the furnace airflow, making it difficult for the equipment to supply the home with enough heat. In this case, a cleaning procedure would be the best solution.

Next step: Call a professional who knows how to perform a solid cleaning routine. Call Blue Flame at (206) 388-5667 or schedule a service online.

3. Noisy Furnace

Furnace noises can come in several forms. Some of the most common include:

  • Screeching noises: If you hear a screeching noise emerging from the furnace, there might be a problem with the bearings inside the blower motor. Over time, the bearings can dry, causing them to emit irritating noises.
  • Rumbling sounds: A rumbling noise after a heating cycle means that the burner continues to burn fuel in the combustion chamber, even after the furnace has shut down.
  • Clicking noises: If the furnace’s ignition system struggles to turn on, you might hear a clicking sound from the furnace. Common causes of a malfunctioning ignition system include dirty burners and damaged flame sensors.

Next step: What you do next depends on the furnace noise. For example, if dry bearings cause a squealing, apply synthetic lubricant. However, never DIY a rumbling noise caused by a defective burner. Doing so can create a risk of carbon monoxide poisoning. Call an HVAC technician for a thorough inspection of your furnace.

4. Frequent Cycling

Frequent cycling happens when a furnace turns on after just completing a cycle. There are a few reasons why frequent cycling occurs, including low airflow from dirty filters or blocked air vents. A dirty flame sensor can also affect the furnace cycles.

Next step: If dirty air filters cause your furnace to cycle excessively, changing them can help. For complex problems like filthy flame sensors, it’s best to leave that up to professionals. Call Blue Flame at (206) 388-5667, and we’ll inspect your furnace for cycling issues.

5. A Leaking Furnace

If your furnace leaks water, you could be dealing with a leaky condenser, causing water to wash over the base of the furnace. A leaking furnace can also be caused by a:

  • Blocked drain line
  • Dirty furnace filter
  • Broken humidifier
  • Faulty blower motor

Next step: Consult with an HVAC technician to inspect the furnace and its components so they can identify the source of the leak. Contact Blue Flame to schedule a service.

6. No Heat

Why is your furnace turning on but not providing heat? For a furnace to produce warm air, it relies on a heat exchanger with heated tubes. These tubes receive air, heat it, and distribute it to each room in your home.

Heated tubes require regular maintenance to keep them from cracking. Otherwise, the air inside your house will remain chilly.

Next step: The good news is that sometimes all you must do is change the thermostat setting by switching it to ‘heat.’ This might help the furnace generate heat when the indoor temperature falls below a certain threshold. However, if the heat exchanger is the problem, reach out to our experts for furnace advice and service.

7. Bad Limit Switch

The limit switch in a furnace has two essential functions. The switch regulates indoor temperatures and turns on the blower once the furnace reaches the desired heat.

This switch tells the blower fan when to turn off and on. If the switch malfunctions, the furnace will continue to run even after your home heats. If the furnace runs continuously, it will overheat. A functioning limit switch is essential to keep the furnace from overheating.

Next step: If something goes wrong, the safest solution is to have a qualified technician replace the existing switch. While you can replace it yourself, furnaces run on high-voltage electricity, so leave it to the experts instead.

8. Broken or Loose Belts

A belt connects the blower to the motor inside the furnace. If the belt loosens, the furnace won’t circulate hot air. Fortunately, it’s easy to detect a broken or loose belt.

If you hear a squealing noise coming from the furnace, this is a signal that one of the belts is damaged.

Next step: If the belt is loose, call a professional technician to examine it. By trying to fix it yourself, you could void the manufacturer’s warranty. You’ll also need to call a technician to replace a broken belt.

9. Dirty Filters

For a furnace to perform efficiently and distribute warm air, it needs clean filters. If the filters clog with dust or dirt, your HVAC system will operate harder than it should, causing a breakdown.

Next step: An easy solution is to replace the dirty filters with new ones. You should replace your filters at least every 90 days, but many homes require more frequent changing, depending on things like pets and indoor air quality. Your Blue Flame HVAC technician can tell you what’s best for your home.

10. No Furnace Air

Sometimes, the furnace may not blow any air, leaving you without a functioning appliance. If this is the case, you could be dealing with one of several issues:

  • A dead thermostat battery
  • Incorrect thermostat time settings
  • A thermostat not set to heat mode
  • A broken blower fan

Next step: If you have dead thermostat batteries, replace them with new ones. If the furnace doesn’t blow warm air, change the settings on the thermostat to heat mode.

For issues like a broken blower fan, call Blue Flame at (206) 388-5667, and we’ll send a qualified HVAC technician to conduct a repair service.

11. Gas Leak

Approximately 47% of U.S. households use natural gas as their primary heating fuel source. If you rely on natural gas, there’s always the risk of a gas leak. What causes a leak? Some of the main reasons include:

  • Clogged drain system line
  • Damaged heat exchangers
  • Broken flame sensors

How can you tell if there’s a gas leak? Do you notice a hissing sound from the furnace? Do you detect a foul odor? If so, it could be a gas leak.

Next steps:

  1. Open doors and windows
  2. Evacuate your home
  3. Turn off the main gas valve to prevent more leaks
  4. Call 911
  5. Contact a local HVAC company for immediate assistance

Contact Blue Flame for All Your Furnace Needs

If you have furnace problems, Blue Flame is up for the task. Call our professionals to schedule a service at (206) 388-5667.


How Much Does It Cost to Check a Furnace?

Furnace repair depends on the type of furnace and what work is required. Here at Blue Flame, you can take advantage of two FREE preventative maintenance visits every year with the Pro Service Plan. We prioritize our client’s financial needs regarding services and replacements.

Take advantage of our guarantee that adds peace of mind when dealing with HVAC-related problems.

How Often Do Furnaces Need to Be Replaced?

The general lifespan of a furnace is between 10 to 15 years. However, this is an estimate; the exact figure depends on:

  • Furnace type
  • Maintenance history
  • Frequency of use

What Are the Signs a Furnace Needs to Be Replaced?

There are a few ways to tell if you need a replacement:

  • Energy bills have increased
  • The equipment makes noises
  • Indoor air quality is poor
  • You’re constantly scheduling repair services

Last Updated: January 12, 2024