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Heating Pipes Making Gurgling Noise? Here’s Why + How to Fix

Gurgling heating pipes are both annoying and a sign of a potential problem. As such, it’s important you get to the bottom of the issue as quickly as possible.

Your heating pipes are gurgling because the air inside the pipes obstructs the water flow. Air can fill the heating pipes due to low boiler pressure, leakage in the piping, and hydrogen forming due to old and rusty pipes. You will need to bleed the system and remove the air to stop the noise.

In this article, I’ll give you a detailed breakdown of why your heating pipes might fill with air and make gurgling noises. After that, I also share a detailed guide on stopping the gurgling noise, along with a few tips to prevent this from happening in the future.

Why Do Heating Pipes Keep Filling With Air?

If you find your heating pipes gurgling, there’s likely a high amount of air inside the piping. The air makes it difficult for the water to flow smoothly through the pipes, resulting in gurgling noise. But how did the air get inside the heating pipes in the first place?

Here are 3 reasons why heating pipes keep filling with air:

  • Not enough pressure
  • Leakage somewhere in the central heating system
  • Hydrogen formation because of rusty piping

Let’s go over each of these points in more detail.

Not Enough Pressure

The most common reason for air filling up heating pipes is a lack of pressure in the heating system. You see, as the water circulates through all the healing pipes, it slowly leaks out through the various pump seals, joints, and valve stems.

This sort of leakage is absolutely normal and expected. The boiler has a feed valve to let fresh water into the system to make up for the lost water. The only problem is that fresh water contains dissolved air.

Now, if the pressure inside the heating system is low, the dissolved air inside the fresh water will come out and start circulating inside the piping. Gradually, the air will start obstructing the water flow, causing the gurgling noise.

Ideally, your heating system should operate at 22-29 psi (1.5-2 atm). Problems arise when this value dips below 14 psi (1 atm).

So why does pressure drop inside the heating system?

Well, the most common reason for pressure drops in heating systems is if you have a leakage. As such, you’ll first need to find and stop the leakage and then re-pressurize the heating system to fix the problem.

For reference, here’s a quick 1-minute YouTube video on how to increase boiler pressure:

Other than that, if you incorrectly bleed the system, that can also result in lower pressure. To fix this, you’ll need to correctly bleed your system and then re-pressurize it.

Later, I’ll run you through a detailed guide on correctly bleeding your heating system.

Leakage Somewhere in the Central Heating System

As I’ve said, having a leakage will reduce the pressure inside the heating system, which releases the dissolved, trapped air inside the water, causing the heating pipes to fill up with water. But that’s not the only way a leakage causes air to fill up your piping.

You see, as the water leaks out of the system, it creates a negative pressure inside the piping, causing the surrounding air to seep in through the crack.

Apart from releasing the trapped air inside the water, a leak will also draw in outside air into the pipes.

Now, diagnosing a leakage is pretty easy. If you notice that the pressure in your central heating system is consistently dropping, it’s a telltale sign you have a leakage (even a very small one) somewhere in the central heating system — either with the piping, valves or on one of the radiators. 

If you suspect a leakage, you can follow this guide on finding and fixing leaks in your heating system.

The gurgling noise should stop once the leak is sealed up and the system re-pressurized.

Hydrogen Formation Because of Rusty Piping

Sometimes, the air in the heating pipes and the heating system doesn’t come from outside. Instead, it can be generated from within the system. If the heating system is old and poorly maintained, the internal components have likely corroded and started to rust. 

Now, hydrogen is a by-product of metallic corrosion and the rusting process. And since hydrogen is a gas, it’ll behave like air and interfere with the water flow, resulting in the gurgling noise.

But how do you know it’s actually hydrogen and not plain air gurgling inside the piping?

Well, here’s a quick test you can perform:

  1. Open the bleed valve on the radiator where you’re hearing the gurgling. Air or hydrogen will come out, making a hissing sound. 
  2. Take an upside-down cup and hold it over the valve to catch some leaking gas.
  3. Light a match and hold it under the cup.
  4. If the cup contains hydrogen (which is flammable), you’ll hear a quick pop as the gas bursts into flame. But if nothing happens and the match burns normally, it’s just air.

If the gurgling sound is due to hydrogen formation, you’ll need to replace all the old and rusting parts to fix the issue.

How To Stop Heating Pipes From Gurgling

Your heating pipes are gurgling because of trapped air. As such, if you want to stop the gurgling, you’ll have to bleed your central heating system and remove all the air out of it.

Now, bleeding your heating system is a straightforward process and something you can do by yourself. You’ll need a screwdriver, a bucket for collecting water, and a towel to clean up any spilled water and handle hot objects safely.

(Quick disclaimer: Although bleeding a heating system is simple, you should exercise some caution. After all, you’ll be dealing with hot water, and if you’re not careful, you can get burned. If you’re not sure how to go about this fix, I recommend contacting a professional instead.)

Once you have everything you need, you can follow this step-by-step guide to help you bleed your heating system:

  1. Start the central heating system and put it on max heat.
  2. Let the system run for 15 minutes, ensuring the hot water and the trapped air flow through all the piping and radiators in your home.
  3. After 15 mins, switch off the heating system to stop the circulation.
  4. Wait another 15 mins to let everything cool down. There’s no need to wait until it cools down to room temperature. You’re just cooling it down, so you don’t have to deal with very hot water.
  5. Go to the radiator closest to the boiler and turn off the radiator valve. 
  6. Put a bucket underneath the bleed valve.
  7. Using the screwdriver, slightly turn the bleed valve anti-clockwise to open it. Do not open it fully.
  8. You’ll hear a hissing sound indicating that air is escaping or “bleeding” from the system.
  9. After the air escapes, water will start coming out of the bleed valve.
  10. Keep the bleed valve open until all the water comes out. When you see no more water, close the bleed valve.
  11. Go to the next closest radiator and repeat steps 6 to 10.
  12. Do this for all the radiators in your home, starting with the ones closest to the boiler.
  13. After bleeding out all the radiators, turn on the central heating system.
  14. Ensure the pressure is between 22-29 psi (1.5-2 atm). If the pressure is lower than that, rebalance it until it reaches that level.

And that’s it! You have successfully bled out your heating system and removed all the trapped air. This should stop your heating pipes from making that annoying gurgling noise.

How To Prevent Heating Pipes From Filling Up With Air

If your heating pipes are gurgling, it’s most likely filled with air. To stop the gurgling noise, you need to bleed the air out, and it should go back to silently heating your home.

But is there a way to prevent the heating pipes from filling up with air in the first place?

Unfortunately, no. There’s no way to absolutely stop air bubbles from forming inside the heating pipes. 

That said, you can take measures to reduce the rate at which air fills up the pipes. It might be just what you need to prevent the annoying gurgling sound you keep hearing every few months.

To prevent heating pipes from filling up with air, here’s what you can do.

Routinely Bleed Your Heating System 

Air will eventually and inevitably get inside your heating system and into your heating pipes. As such, it’s a good idea to routinely bleed your heating system and not wait for the “gurgling” alarm to tell you it’s time. Ideally, you should bleed the system right before and after the winter season.

Removing all the air in the heating system before winter ensures you won’t have to worry about gurgling noises throughout the full length of the cold months.

During the winter, the pipes have likely filled up with some air. So, when winter is over, give the system another bleed to ensure there’s no air inside it while it sits idle for several months. This can help prevent corrosion and potentially extend the heating system’s life.

Get Your Heating System Annual Servicing

Certain faults, defects, and irregularities in the heating system can cause air build-up and a whole host of problems. As I mentioned earlier, rusty pipelines or malfunctioning pumps can cause air build-up inside the system, eventually causing that annoying gurgling noise.

As such, routinely servicing your heating system is super important. 

Ideally, you should have the heating pipes, radiators, boiler, and all other parts of the system checked by an HVAC technician at least once a year — preferably before winter starts. Doing this will let you know about any faulty parts before they cause any problems.

Install an Automatic Air Bleeding Valve

An automatic air bleeding valve is a small apparatus that typically fits in your radiator and helps expel the trapped air inside it. When your heating system is filled, the valve automatically opens to bleed out the air until the water reaches it. Once that happens, it’ll close itself.

Now, the rate at which it bleeds out air is somewhat slow, and it won’t work if the heating system lacks pressure. Furthermore, it’s only effective at bleeding out excess air collected in the radiator and won’t help you remove dissolved air in the water.

That said, it’s still an excellent tool for keeping your heating system air-free. 

For reference, here’s a quick 4-minute YouTube video demonstrating how these auto air vents work:

Install an Air Separator

Air separators are typically installed in chilled water systems, but they can also help with hot-water systems, especially if you have a persistently recurring gurgling issue. Be aware that there are different types of air separators — each of which works differently and is designed to cater to different issues.

In this case, you want to remove air build-up in the heating pipes and the heating system to avoid the annoying gurgling noises. For this, you can opt for ASME tangential air separators.

These devices efficiently separate and remove any air in water flowing through a closed heating system (or cooling system). They create a low-velocity swirling vortex to separate the air from the water.

Key Takeaways

The main reason your heating pipes are gurgling is that there’s air inside the piping interfering with the water flow. Air usually builds up inside heat pipes because of low pressure, leakage, or old and rusty piping releasing hydrogen into the system.

The gurgling noise should stop once you bleed out all the trapped air inside the heating system.

To prevent gurgling heating pipes in the future, I recommend you routinely bleed the system, get annual maintenance checks, and install an automatic air bleeding valve and an air separator.


  • 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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