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Furnaces Making a Rumbling Noise? 5 Common Causes and Fixes

Your furnace must produce some sounds as it’s heating your house. The noise levels depend on several factors, such as how old it is. But if you hear a concerning rumbling noise coming from the furnace, it’s time to investigate.

Your furnace is making a rumbling noise because it’s dirty, there are loose panels, or you have a faulty heat exchanger or pilot light. Stop the rumbling noise by cleaning the gas burners and inducer motor, replacing or fixing the pilot light and heat exchanger, and tightening loose panels.

This article will explain all the possible causes behind the rumbling noise and how to perform a step-by-step diagnosis to find the cause. I’ll also discuss what the best solution is for each problem.

Loose Panels

Loose panels are the most common cause behind a rattling or rumbling sound. Screws loosen up over time, so the metal sheets start to vibrate while the furnace is running. Thankfully, the solution is super simple.

How To Fix

Check all the panels outside your furnace to see whether they’re fitted correctly.

If you found a loose panel, use a screwdriver to tighten all screws. 

If you don’t have a ratcheting screwdriver, you’re missing out! I recommend the SATA Multipurpose Ratcheting Screwdriver Set (Amazon.com). You can choose from different piece sets. As a nice bonus, the handle is oil-resistant.

Restart your furnace and see if you can still hear the rumbling noise.

Faulty Pilot Light

The pilot light’s job is to ignite the gas from the furnace’s burner. The heat then warms the air that circulates through a network of ducts and vents to provide heat throughout your building. 

Electrical igniters have replaced pilot lights in modern furnaces, but older models still rely on a pilot light.

A sooty or dirty pilot light will produce a split flame, while a well-functioning light will produce a blue flame. Any other color indicates a problem in the furnace. A sooty pilot light could cause your furnace to continue heating up in the combustion chamber long after the heating cycle completes.

How To Fix

Here are the steps to clean your pilot light:

  1. Turn off the power and gas supply to your furnace.
  2. Remove the pilot light’s cover.
  3. Use a wrench to remove the nuts that fix the pilot light and thermocouple in place. You can use the Crescent 6″ Adjustable Wrench (Amazon.com) for this. It’s resistant to corrosion, has a non-slip grip handle, and you can use it for different fastener sizes.
  1. Detach the pilot light from the gas supply line
  2. Use a soft bristle wire brush to clean any soot or debris from the pilot light. The Long Straw Brush (Amazon.com) is perfect for cleaning the tube efficiently.
  3. Use an air compressor to blow the dirt off the pilot light
  4. Reinstall the pilot light.
  5. Check your pilot light; does it look too high or low? A misaligned pilot light will not light the gas efficiently, resulting in a rumbling noise.

If your pilot light is misaligned, here’s how to adjust it to the correct position:

  1. Check your user manual to see if it mentions the pilot light’s position.
  2. Turn off the power and gas supply to your furnace.
  3. Locate the pilot valve. It has a small screw that, when turned, will adjust the pilot flame.
  4. Use a screwdriver to turn the screw until the flame is in the correct place.

These steps should be easy if you’re a DIYer. Otherwise, it’s safer to call a qualified furnace technician to fix the pilot light for you. Also, consider replacing the furnace altogether to get better efficiency.

Dirty Gas Burners

You need to clean your gas burners regularly to prevent soot buildup as it limits airflow for combustion. A gas burner produces an explosive or rumbling sound when it’s trying to ignite. The sound will continue even during operation.

How To Fix

There are several steps to clean your burner:

  1. Cut off the power supply to the furnace and wait a few minutes for the remaining gas to drain out and the electric current to dissipate.
  2. Use a screwdriver to detach the burners’ screws and remove the burners. Depending on the model you have, the burners will come off all at once or individually. Some burners won’t come off the furnace, but you can clean them without removing them.
  3. Use a long soft bristle brush to clean any dirt and soot off the burners.
  4. Use a shop vacuum to clean out any debris in the burner and around the furnace.
  5. Locate the gas jets in every burner and detach them from the gas line.
  6. Push a thin wire brush through the jets to clean out any leftover debris.
  7. Place the jets in their original position and screw them tight.
  8. Place the burners back and fasten them.
  9. Restart the furnace to check whether the problem is gone.

Watch this video by Word of Advice TV if you’re having trouble cleaning the burners:

Dirty Draft Inducer Motor

You can find the inducer motor next to the heat exchanger in your furnace. The motor ensures that your furnace works efficiently by directing all the furnace’s by-products, like harmful gases, out of your building through the flue pipe.

The motor also supplies the burners with fresh oxygen to ensure that the furnace’s gas is heated effectively.

How To Fix

I don’t recommend cleaning the inducer motor yourself — an untrained eye won’t notice specific issues. Please contact your nearest HVAC technician to repair the inducer motor. In some cases, you’ll have to replace it.

AMRE Supply’s video can tell you more about the inducer motor:

Cracked Heat Exchanger

The heat exchanger consists of an array of coils that do the actual heating. The heat exchanger can crack from overheating. If your heat exchanger is cracked, you’ll notice soot inside the furnace in addition to the rumbling sound. 

This means that gas isn’t getting burned effectively. You’ll notice corrosion and cracks on the furnace’s devices and sometimes even water on the floor.

How To Fix

Cracks in the heat exchanger are hazardous — the gases can cause carbon monoxide poisoning and even explode. In most cases, you can tell that your heat exchanger is cracked if your smoke detector detects carbon monoxide.

This situation requires immediate assistance from a technician. Turn everything off and call them to come to take a look at your furnace.

Perform Routine Maintenance Checks

Because of the significance of heating systems, especially in colder climates, you must schedule routine maintenance checks, especially before winter.

A timely inspection will save you money by preventing substantial malfunctions that require the replacement of furnace parts.

Final Thoughts

Throughout this article, you have learned the potential causes of a rumbling sound in a furnace. You now know how to find the components that can cause the noise and fix them.