How To Clear An Air Lock In A Central Heating System

Learn how to clear an air lock in your central heating system. Follow step-by-step instructions and get your system running smoothly again. Say goodbye to cold showers and chilly nights!

So, you’ve been experiencing some issues with your central heating system lately, huh? Well, fear not, because we’re here to help you out. In this article, we’ll teach you the simple but effective steps to clear an air lock in your central heating system. Whether you’re freezing in the dead of winter or just eager to stay cozy, this quick solution will have your system up and running smoothly in no time. Say goodbye to cold showers and chilly nights, and let’s get started on unlocking the warmth in your home!

Tools and Materials

To clear an air lock in a central heating system, you will need the following tools and materials:

Bucket or container

You will need a bucket or container to collect any waste water that may be released during the process.

Cloth or towel

Having a cloth or towel handy will allow you to clean up any spills or messes that may occur while working on the heating system.


A hosepipe is essential for connecting to the system and allowing water to flow through it to clear the air lock.

Spanner or adjustable wrench

A spanner or adjustable wrench will be necessary for opening and closing the air bleed valve, which is a critical step in the process.


A screwdriver may be necessary for loosening any screws or fittings that are blocking access to the air bleed valve or other components of the system.

Plastic bag or container for waste water

A plastic bag or container is useful for collecting any waste water that may be expelled during the air lock clearing process, helping to keep your workspace clean and tidy.

Now that you have your tools and materials ready, let’s move on to identifying an air lock in your central heating system.

Identifying an Air Lock

Before you can clear an air lock, you must first identify whether you have one in your central heating system. Look out for the following signs:

Lack of circulation in radiators

If you notice that some or all of your radiators are not heating up or have cold spots, this may be an indication of an air lock. When air is trapped within the system, it can prevent water from circulating properly and reaching all areas of the radiator.

Unusual noises or gurgling sounds

If you hear gurgling sounds or noises coming from your heating system, it could be a sign of air bubbles trapped in the pipes or radiators. These air bubbles can disrupt the flow of water and cause the system to make unusual sounds.

Cold spots on radiators

When air becomes trapped in a radiator, it can result in cold spots where the radiator is not heating up as it should. If you notice areas of your radiator that are cold while the rest is warm, an air lock may be the culprit.

Inadequate heat output from radiators

If your radiators are not providing enough heat or are not reaching the desired temperature, it could be due to an air lock. When air is trapped within the system, it reduces the efficiency and effectiveness of the heating process.

Now that you have identified an air lock, let’s move on to the step-by-step instructions for clearing it.

Step-by-Step Instructions

Follow these step-by-step instructions to clear an air lock in your central heating system:

1. Switch off the central heating system

Before you begin, make sure to switch off the central heating system. This will ensure that no hot water is circulating through the system while you are working on it.

2. Locate the air bleed valve

Next, locate the air bleed valve in your central heating system. This valve is usually located on the radiator, near the top and on the side. If you are unsure, consult your heating system manual or seek professional advice.

3. Prepare for the task

Place a bucket or container below the air bleed valve to catch any waste water that may be expelled during the process. Also, have a cloth or towel handy to clean up any spills or drips.

4. Connect the hosepipe

Attach one end of the hosepipe to the air bleed valve, ensuring a tight and secure connection. Place the other end of the hosepipe into the bucket or container that you have prepared.

5. Open the air bleed valve

Using a spanner or adjustable wrench, slowly loosen and open the air bleed valve. You may hear a hissing sound as air begins to escape from the system. Allow the air to release until you see a steady flow of water coming out of the valve.

6. Check the pressure gauge

While the water is flowing through the system, keep an eye on the pressure gauge. The pressure should remain within the recommended range for your specific central heating system. If the pressure drops too low or rises too high, it may indicate another issue that requires attention.

7. Allow water to flow through the system

Continue to let water flow through the system until you no longer see any air bubbles in the water. This indicates that the air lock has been successfully cleared.

8. Close the air bleed valve

Once the air lock has been cleared and only water is coming out of the air bleed valve, use a spanner or adjustable wrench to close the valve securely.

9. Monitor the pressure gauge

After closing the air bleed valve, monitor the pressure gauge to ensure that the pressure remains stable within the recommended range. If you notice any drastic changes in pressure, you may need to address other issues with your central heating system.

10. Switch on the central heating system

Finally, switch on the central heating system again, and check that all radiators are heating up evenly. If the air lock has been successfully cleared, you should now have proper circulation and adequate heat output throughout your system.

Alternative Methods

While the above step-by-step instructions are a commonly used method for clearing air locks in central heating systems, there are alternative methods that you can consider:

Using a drain cock

In some heating systems, there may be a drain cock that can be opened to release any trapped air. This method requires specific knowledge of your heating system and its components, so it’s essential to consult your heating system manual or seek professional advice before attempting this method.

Using a pressurized system

Some pressurized central heating systems have an automatic air vent that releases trapped air. If your system has this feature, it may be a matter of waiting for the air vent to do its job. However, if the problem persists or worsens, it may be necessary to seek professional help.

Using a power flush

If none of the above methods are successful in clearing the air lock, a power flush may be required. A power flush involves using specialized equipment to force water through the system at high pressure, dislodging and removing any trapped air or debris. This method is more complex and should be carried out by a qualified professional.

Preventive Measures

To prevent future air locks in your central heating system, consider implementing the following preventive measures:

Regular maintenance

Regularly maintaining your central heating system can help prevent the occurrence of air locks. This includes bleeding radiators annually, inspecting and cleaning system components, and addressing any issues promptly.

Balancing the radiators

Properly balancing your radiators ensures that hot water is evenly distributed throughout the system. Balancing involves adjusting the flow of hot water to each radiator, allowing for more efficient and effective heating.

Installing a bypass valve

Installing a bypass valve allows hot water to flow around a specific radiator, preventing it from becoming airlocked. This can help maintain consistent heating throughout the system.

Using chemical inhibitors

Adding chemical inhibitors to your central heating system can help reduce the formation of sludge and air bubbles, therefore minimizing the likelihood of air locks. Consult a professional for advice on the appropriate inhibitors for your system.

Seeking Professional Help

While clearing an air lock in a central heating system can often be done by following the above instructions, there are situations where professional help may be required:

Persistent airlock problems

If you have attempted to clear the air lock multiple times but it continues to reoccur, or if you consistently have multiple air locks in your system, it may indicate a more significant underlying issue. In such cases, it is advisable to seek the assistance of a qualified heating engineer.

Complex system

If you have a complex central heating system, such as a multi-zone or underfloor system, it can be challenging to locate and clear air locks effectively. A professional with the necessary expertise and knowledge of these systems will be able to assist you.

Limited technical knowledge

If you are unfamiliar with the workings of your central heating system or lack confidence in carrying out the tasks involved in clearing an air lock, it is recommended to consult a professional. They will have the knowledge and experience to address the issue safely and efficiently.


Clearing an air lock in a central heating system is a task that can be accomplished with a basic understanding of the system and the right tools. By following the step-by-step instructions provided and considering preventive measures, you can effectively resolve and prevent air locks, enabling your central heating system to provide efficient and consistent heat throughout your home. Remember to seek professional help if needed, especially in complex systems or persistent airlock situations. With proper maintenance and periodic checks, you can ensure the optimal performance and longevity of your central heating system.

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