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

So, you’re concerned about gurgling noises that sound like boiling water coming from the furnace? In some cases, a gurgling sound is a normal part of the startup process, but you should understand when it isn’t. The sound indicates potential problems with condensation pipes, and the last thing you want is water to get to your HVAC’s electrical components.

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 lines and replacing the condensate pump.

This article provides a complete overview of the most common causes behind a gurgling sound coming from an HVAC system. We’ll go over how to diagnose the source of the problem and how to fix it. 

Blocked Condensation Pipes

The furnace uses pipes to transport condensation out of the system and ensure water doesn’t leak from the air vents. The pipes 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 important step in determining if this is the source of the gurgling noise you hear. Here’s what you need to do: 

  1. Turn the furnace off. If possible, unplug the furnace completely.
  2. Remove the condensate pipes from the trap. This should be a straightforward process. If you’re having difficulties, refer to the owner’s manual. 
  3. Take the pipes out of the furnace. 
  4. Take a look at the pipes and see if you can find any blocked parts. You can run some water through the pipes to see if it passes through without any problem. 

If water doesn’t run through completely 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: 

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 faulty 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: 

Excessive Condensation in the Furnace

As we already established, 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 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, 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. A certified HVAC specialist can also look at the interior components while the furnace is running to see what part is causing the problem.

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. 


Sometimes, a gurgling sound in a furnace may be normal, but only if it’s very subtle and happens for a few seconds when you first turn the furnace on. But when the sound is loud and just keeps going, you need to look at possible problems.


  • Nicole Sutton

    Nicole Sutton is an enthusiastic writer and knowledgeable contributor to 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.