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Furnace Making Gurgling Noise? (Causes & Solutions)

Your furnace is making a gurgling noise because the condensation pipes are blocked, the condensate pump is faulty, there’s excessive condensation in the furnace, or there are problems with the refrigerant lines. Fixes include fixing faulty pipes and tubes and replacing the condensate pump.

After studying the operations of a HVAC system maintenance shop, we observed that the issue of furnaces making a gurgling noise was among the most common problems that many homeowners call in to troubleshoot. So, if you’re currently experiencing this, there’s no need to panic. 

This article will show you the most common causes behind a gurgling sound coming from an HVAC system. You will learn how to diagnose the source of the problem and how to fix it. In some cases, a gurgling sound is a normal part of the startup process, but you should understand when it isn’t.

Understanding the Gurgling Noise

The gurgling sound coming from your gas furnace will sound like running water, making the air exhaust pipe sound like a water pipe. 

In many cases, the sound comes from the combustion vent pipe that is going from the HVAC to the roof. If it has been a cold climate in the last few days, it’s easy to suspect the sound comes from the moisture steam condensing inside the pipe and flowing back to the HVAC. 

But if you can see steam coming out from the vent exhaust on the roof, it means the pipe is not blocked. So, a possible explanation is that the noise is caused by a plugged drain from the furnace, making it unable to drain correctly. So, the air-moving inducer motor is now acting as a paddle wheel. 

By all indications, a gurgling nose from a furnace becomes a severe worry when the noise is accompanied by other symptoms such as strange smells, pilot light issues, or loss of heat. Any signs of moisture leakage around the furnace or heating system also pose a serious concern.

Troubleshooting Gurgling Noise from Furnace – Step-By-Step Guide 

Follow these steps to troubleshoot and fix the gurgling noise from your HVAC system: 

1. Checking for Air in the System 

Air trapped in your furnace system can lead to gurgling noises, disrupting its smooth operation. 

How to fix

  • Begin by locating the air bleeder valve, often situated near the high points of the system.
  • Using a wrench, slowly open the valve to release any trapped air.  
  • Listen for the hissing sound of escaping air and continue until water begins to flow steadily. 
  • Close the valve tightly once the air is purged. 

2. Inspecting the Condensate Drain Line 

The furnace uses pipes to transport condensation out of the system and ensure water doesn’t leak from the air vents. The lines run out of the furnace toward a “condensate trap” — a small structure that “traps” the condensate water. 

Note that condensation happens when air is heated — this means the collected water is likely quite warm. If there’s a water build-up in one spot, you may hear a gurgling sound. 

This build-up of condensate liquids can occur if the pipes that carry the water toward the condensate trap are blocked. A blocked pipe can also increase pressure in the rest of the condensate assembly, resulting in problems if no action is taken. 

How To Fix

Inspecting the condensate pipes is an essential step in determining if this is the source of the gurgling noise you hear. Here’s what you need to do: 

  • Turn the furnace off. If possible, unplug the furnace completely.
  • Remove the condensate pipes from the trap. This should be a straightforward process. If you’re having difficulties, refer to the owner’s manual. 
  • Take the pipes out of the furnace. 
  • Take a look at the pipes and see if you can find any blocked parts. You can run some water through the lines to see if it passes through without any problem. 
  • If water doesn’t run through entirely or the stream coming out on the other end is weak, it means something is blocking the flow.

You may have to take the pipe apart. You can easily see where the different parts of the pipe fit together. Do this until you find the blockage. Try to remove the item that’s blocking the flow of water. 

Here’s a video that’ll teach you how to clean your furnace’s condensate pipes: 

3. Faulty Condensate Pump

The condensate pump may also be at fault if you hear a gurgling sound coming from the furnace. This is because a failing condensate pump leads to condensate buildup inside the furnace. The pump is responsible for sucking in the condensate water and sending it through the condensate pipes toward the trap. 

A faulty condensate pump could spell trouble for the furnace. It increases the chances of liquids coming into contact with electronics. Depending on the problem, a defective pump can be accompanied by additional noises. 

How To Fix

It’s sometimes possible to fix a faulty condensate pump, but it depends on the problem at hand. However, in most cases, you should consider getting the pump replaced. While this may be a more expensive option today, it can save you a lot of trouble and money in the long run. 

The condensate pump has a box-like structure. It’s attached to the pipes coming from the furnace. Pipes that come out of the pump then run to the trap. 

For details on how to replace the condensate pump, take a look at the video below: 

4. Excessive Condensation in the Furnace

When there’s too much condensation inside the furnace, you’re likely to hear a gurgling sound. This problem can be diagnosed by opening up the main panel on the furnace and looking inside. 

In addition to a gurgling sound, you may also hear dripping inside the furnace — this happens when liquids start accumulating at the top of the furnace and then drip down. 

There are a few reasons why there may be increased condensation inside the furnace. In addition to problems with the condensate lines and pump, you should also check the hardware inside the furnace. 

How To Fix

You need to find the root of the problem before any fixes can be initiated. This means turning off the furnace and taking a close look inside. 

In this situation, we recommend having a certified HVAC specialist look at the interior components while the furnace is running to see what part is causing the problem.

5. Problems With the Refrigerant Lines

Another reason for an HVAC system to cause a gurgling sound may be related to the refrigerant lines. Note that this doesn’t apply to a heating system that only consists of a furnace. 

But most homes in the US do have a complete HVAC system. In other words, you have an air conditioning unit (AC).

The refrigerant lines help with cooling and the dehumidification process that creates condensation. Sometimes, however, liquids get stuck inside these lines. This can happen when there’s a problem with the refrigerant line sealing. 

When something gets stuck and you turn the furnace on, the furnace’s heat can create a gurgling sound. 

While this isn’t the most common reason for a gurgling noise, it’s still something you want to consider if you have an AC and furnace as part of your HVAC solution. 

How To Fix

Closely inspect the refrigerant lines if you suspect they might be behind the gurgling sound. 

You might have to remove the lines to investigate. But first, start the process by turning the furnace on. Don’t remove anything just yet; simply stand close to the lines and see if you hear the sound coming from the pipes. If this is the source, turn off the furnace and inspect the refrigerant lines.

Look at how the pipes are installed and check if they’re damaged. Make sure there are no cracks or bends. These pipes need to be sealed effectively. Otherwise, liquids may move into your furnace’s electronics. 

6. Flushing the Condensate Trap 

The condensate trap is susceptible to sediment accumulation, impeding proper drainage and causing gurgling noises. 

To remedy this, locate the trap and carefully remove it. Flush the trap with a mixture of water and mild detergent to dislodge any sediment. 

Allow the trap to air dry thoroughly before reattaching it. 

Pro Tip: 

  • Regular flushing of the condensate trap prevents blockages. That will allow efficient water drainage and eliminate gurgling disturbances. 

7. Cleaning the Heat Exchanger 

A dirty or clogged heat exchanger can contribute to gurgling sounds in your furnace. Turn off the furnace and carefully inspect the heat exchanger for any visible debris. 

Use a soft brush or compressed air to clean the surfaces gently; ensure the furnace is completely cooled before attempting any cleaning. 

The video below provides extra guidelines on the procedure for cleaning the heat exchanger of the furnace to get rid of the gurgling noise that this issue produces:

8. Examining the Water Level in the Humidifier 

If your home has integrated humidifiers, an incorrect water level can result in gurgling sounds. 

Check the water reservoir and adjust the water level according to the specifications. 

Inadequate or excess water in the humidifier can disrupt the balance within the system, causing unusual noises. 

9. Adjusting the Water Pressure 

In some instances, imbalanced water pressure can lead to gurgling noises in the furnace. Locate the water pressure regulator and adjust it to achieve the recommended pressure level.

Your furnace manual or manufacturer guidelines will have instructions for the appropriate pressure range. 

10. Seeking Professional Assistance 

No one likes to book a service appointment if they don’t need to. But as you troubleshoot, remember that a noisy furnace can turn into a more significant issue than it seems at first. 

The furnace might be working fine otherwise, but the condensation problem or leak could be slowly ruining parts and leading to a significant breakdown. 

If the above-listed steps don’t stop the noise you’re hearing or if you notice rust or damaged parts on the furnace, we recommend you book a maintenance inspection. 

Professional HVAC technicians also have the tools necessary for all kinds of plumbing repairs, including installation, and can use them without causing damage. 

If you’re new to your neighborhood, you can search for “HVAC technician near me” on Google with your location turned ON to find the nearest service around. 

Preventive Maintenance Tips Against Furnace Gurgling Noise 

We recommend you incorporate these checks into your routine maintenance:

Maintenance TipsDirection
Check the condensate drain lineThe condensate drain line carries away water produced during the heating process. It should be free from clogs or blockages. If clogged, clean it by using a mixture of water and vinegar or a specialized condensate line cleaner.
Monitor humidity levelsMaintain appropriate humidity levels in your home. Excessive humidity can lead to condensation issues within the furnace, causing gurgling sounds. Use a dehumidifier if needed to control indoor humidity.
Replace air filtersRegularly replace or clean the furnace air filters to ensure proper airflow. Clogged filters can lead to condensation and gurgling noises. Follow the manufacturer’s recommendations for filter replacement.
Don’t ignore water leaks.If you notice water around the furnace, investigate it promptly. Leaks can lead to gurgling noises and may indicate a problem with the condensate drain system.
Install a condensate pumpIf your furnace is located in a basement or below ground level, consider installing a condensate pump to help remove water effectively.

Author

  • Nicole Sutton

    Nicole Sutton is an enthusiastic writer and knowledgeable contributor to TemperatureMaster.com. She offers a plethora of knowledge to the platform, with a background in environmental science and a profound curiosity with all things connected to temperature regulation. Nicole's interesting and informative writings assist readers in making informed decisions about home heating, cooling, and climate control.

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