Furnace Making Gurgling Noise? 4 Common Causes (+ Fixes)

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A gurgling noise may cause concern, with many people thinking that water is boiling inside the furnace. In some cases, a gurgling sound is a normal part of the startup process, but you should understand when it is not. The sound may signal condensation problems, and you do not want the liquid to move toward your HVAC’s electrical components.

To fix a furnace making a gurgling noise, see if something is causing a blockage in the condensation pipes, make sure the condensate pump is not faulty, check for excessive condensation in the furnace, and check the refrigerant lines for problems. 

This article provides a complete overview of the reasons for a gurgling sound to come from an HVAC system. We look at ways to diagnose the source of the problem and tell you how to fix it. 

The Condensation Pipes Are Blocked

The furnace uses pipes to transport condensation out of the system itself and ensure water does not leak from the air vents. The pipes run out of the furnace and toward a “condensate trap” – a small structure that helps to “trap” the condensate liquids. 

Take note that condensation happens when the air is heated – and this means the liquid produced is likely to be warm, depending on the temperature settings on your thermostat. If there is a build-up of liquids 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 is 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 important step to help you determine if this is the source of the gurgling noise you hear. For this step, the furnace should be off. You can unplug the furnace if that makes you feel a bit safer too: 

  1. Remove the condensate pipes from the trap. This should be a straightforward process. If you are having difficulty, you can look at an instructional video or refer to the furnace owner’s manual. 
  2. You should also remove the pipes from the area they connect to on the furnace. 
  3. Now, take a look at the pipes and see if you can find any part that is blocked. You can run some water through the pipes and see if it passes through without any problem. 
  4. If water does not run through completely or the stream that comes 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 area where there is a blockage – then attempt to remove the item that is blocking the flow of water. 

Here’s a video that helps you understand how to clear the condensate pipes on your furnace: 

There Is a Fault With the Condensate Pump

The condensate pump may also be at fault when you hear a gurgling sound in the furnace. This is another reason for condensate to build up inside the furnace. This pump is responsible for sucking in the condensation that occurs – the liquid is then sent through the condensate pipes and toward the trap. 

A faulty condensate pump could mean trouble for the furnace. It increases the chances that liquids will come into contact with electrical parts inside the device. A faulty pump can also make additional noises, depending on the specific fault. 

How To Fix

It is sometimes possible to fix a faulty condensate pump, but it depends on the problem at hand. In some cases, however, you want to consider getting the pump replaced instead. While this may be a more expensive option, for the time being, it can save you a lot of trouble, complications, and money in the long run. 

The condensate pump has a box-like structure and is attached to the pipes that come from the furnace. Pipes that come out of the pump then runs to the trap. 

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

Excessive Condensation in the Furnace

When there is too much condensation inside the furnace, then a gurgling sound is also likely to occur. 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 to accumulate at the top of the furnace and then drips 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, also take a look at 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 closer look inside. A certified HVAC specialist can also look at the interior components while the furnace is turned on – this helps them see what parts are causing problems with expelling condensation. 

Problems With the Refrigerant Lines

Another reason for an HVAC system to cause a gurgling sound may be related to the refrigerant lines. You should take note that this does not apply to a system that only consists of a furnace. Many people do, however, prefer the installation of a complete HVAC solution. This means you will have both a furnace and an air conditioning unit installed at home. 

The refrigerant lines help with the process of condensation and the movement of liquids through the system. Sometimes, however, liquids get stuck inside these lines. This often happens when there is a problem with the sealing of the refrigerant lines. When water gets stuck, the furnace’s heat may cause a gurgling sound to develop in the area. 

While this is not the most common reason for a furnace making a gurgling noise, it is still something that you want to consider if you have an AC and furnace as part of your HVAC solution. 

How To Fix

The refrigerant lines need to be inspected closely if you suspect they might be behind the gurgling sound the HVAC system makes. 

You might have to remove the lines to investigate, but first, start the process with the furnace turned on. Do not remove anything 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 look closely at the specific pipes to identify the noise. 

Look for problems with the fitting of the pipe, as well as the structure. Make sure there are no cracks also. These pipes need to be sealed effectively, or liquids may move into areas that should be kept dry. 


Sometimes, a gurgling sound in a furnace may be normal, but only if it is very subtle and happens for a few seconds when the device is started up. When the sound is loud and continues to be present, you need to look at possible problems. 

The form below can help you get in touch with an expert in your local area. We only connect our clients with the most trustworthy HVAC professionals, ensuring you can get your system fixed and the gurgling sound is taken care of efficiently.

Steve Rajeckas

Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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