Facebook pixel
new boiler

Get a new boiler

Fixed price boilers, next day

See boiler prices
new air conditioning

Air Conditioning

Get a quote
new heat pump

Heat Pumps

Coming soon

new ev charger

EV Chargers

Get a quote
boiler servicing

Boiler Servicing

Get a quote

Last updated: 7th May, 2024


How to Fix Boiler Airlock: Expert Guide

How to Fix Boiler Airlock: Expert Guide

Key takeaways

  • Boiler airlocks can hinder the efficiency of central heating systems due to trapped air in pipes and radiators.
  • Detecting airlocks involves observing unusual sounds and uneven heating in radiators; fixing may require bleeding or draining the system.
  • It is crucial to identify when professional help is necessary to avoid damaging your central heating system.

If you're struggling with a boiler airlock, our comprehensive guide can help. We explain the common causes of a boiler airlock and provide step-by-step instructions on how to fix it. We compare advice from reputable sources like Vaillant, Boiler Central, and DoItYourself.com to help you get your heating system running smoothly again.

A boiler airlock can be quite an inconvenience for homeowners, as it hampers the efficient functioning of the central heating system.

Understanding the causes and symptoms of an airlock is crucial for its timely detection and resolution. Typically, airlocks occur due to trapped air in the pipes or radiator, resulting in poor circulation and reduced performance of your heating system.

Need a new boiler?

Get a quote in 60 seconds, fitted as fast as next day!
0% APR finance available.

Get a quote

Detecting an airlock in your radiators may involve listening for unusual sounds like gurgling or trickling, and observing uneven heating across the surface of the radiator.

Once an airlock is identified, there are several methods to fix the issue, including bleeding the radiators or draining the entire system. However, it is essential to know when a professional engineer's assistance is required to safeguard your central heating system and avoid potential damage.

Understanding Boiler Airlock:

A boiler airlock is a common issue faced by many central heating systems. It occurs when trapped air within the system accumulates in a single location, disrupting the consistent flow of water and often leading to various symptoms. In this section, we’ll explore the causes and symptoms of boiler airlock, providing valuable insight into this phenomenon.

Central heating systems rely on a constant supply of water to maintain consistent heating throughout the property. Airlocks can interfere with this process, leading to cold spots on radiators, a lack of hot water from taps, and other issues. Identifying the signs of an airlock is crucial for diagnosing and fixing the problem as soon as possible.

One of the primary symptoms of a boiler airlock is the presence of abnormal noises emanating from the system. Gurgling, hissing, or tapping sounds can be a dead giveaway that air is trapped in the central heating system. These noises can sometimes be overlooked in older systems or mistakenly attributed to normal boiler operation.

Another common symptom of an airlock is a lack of hot water from taps. When air pockets form within the system, they can disrupt the flow of water and prevent it from reaching parts of the property. In some cases, this can manifest as inconsistent water temperatures or sporadic supply of hot water.

In addition to the aforementioned symptoms, banging sounds may also indicate a boiler airlock. As trapped air may cause pressure fluctuations within the system, this can lead to pipes and components making loud tapping or banging noises. These sounds are not only unpleasant but could also indicate potential damage to the central heating system if left unaddressed.

In summary, boiler airlocks are a common central heating system issue that can lead to various problems, such as abnormal noises, uneven heating, and a lack of hot water supply. By understanding the symptoms of an airlock, homeowners and professionals can properly diagnose and fix the issue, ensuring optimal boiler performance and a comfortable living environment.

Detecting an Airlock in Your Radiators

When dealing with a boiler airlock, it's crucial to detect the issue in your central heating system, especially in your radiators. In this section, we'll explore the key indicators that can help you identify if your radiators have developed an airlock.


Key Indicators

  1. Cold radiators: While diagnosing an airlock issue, one of the first things to check is if your downstairs radiators remain cold despite having the central heating system turned on. Typically, trapped air can result in these radiators not heating up as they should.

  2. Hissing sound: Another noticeable sign of an airlock is hearing a hissing sound coming from your radiators when the heating system is active. This may indicate that trapped air is trying to escape through the valves in the system.

  3. Sputtering: If you notice that your radiators are sputtering or making a gurgling sound, this could be an indication that air is trapped within the system. It's vital to address this problem quickly, as it could lead to uneven heating and, potentially, further issues with your boiler.

In order to clear the airlock and restore your radiators to full functionality, you may need to bleed the radiators. Bleeding radiators involves using a radiator key to open the valve at the top of the radiator and allowing trapped air to escape until water flows out. Ensure you have a dry cloth, towels, and a container to catch any water released during this process.

By keeping an eye out for these key indicators, such as cold radiators, hissing sounds, and sputtering, you will be able to confidently detect and address any airlock issues in your central heating system's radiators.

Methods to Fix Airlock

When dealing with a boiler airlock, it is essential to approach the issue with confidence and knowledge. Several methods can be used to fix an airlock in your boiler system, but two of the most common and effective techniques are "Bleeding the Radiator" and "Using the Garden Hose Method". In this section, we will discuss both these methods step by step. It is crucial to use the proper tools and follow safety precautions while performing these tasks.

Bleeding the Radiator

One effective way to fix an airlock is to bleed the radiators in the correct order. Start by switching off the boiler and isolating the electrics to prevent any hazards. While following this procedure, it is essential that the pump is not running.

  1. Prepare the area: Lay a dry towel beneath the radiator you want to bleed to catch any escaping water. Keep a radiator bleed key and additional tools, such as a screwdriver and pliers, handy.

  2. Locate the bleed valve: With the boiler off and the system cooled down for around 20 minutes, locate the bleed valve typically found at the top of the radiator.

  3. Open the valve: Insert the radiator bleed key into the valve and turn it slowly anti-clockwise to release the trapped air. Listen for a hissing sound, indicating the air escaping from the system.

  4. Close the valve: Once the hissing sound stops and water begins to flow from the valve, close it by turning it clockwise. Check and adjust the boiler pressure if necessary and refill the system.

Using the Garden Hose Method

Another approach to fix an airlock involves using a garden hose to dislodge the trapped air. This method requires an outdoor tap and a suitable length of hosepipe.

  1. Prepare the pipework: Turn off the mains water supply and locate the stopcock valve, usually found beneath a kitchen sink. Turn it clockwise to stop the water flow. Open all the hot water taps in your home to drain any remaining water from the system.

  2. Connect the hose: Attach one end of the garden hose to the outdoor tap and the other to the lowest hot water tap in your home, typically located in the bathroom or kitchen. Securely fix the connections with duct tape.

  3. Force water through the pipes: Turn on the outdoor tap, allowing the water to flow through the hose and into the hot water system. The pressure from the hose ought to dislodge any trapped air, clearing the airlock.

  4. Drain and disconnect: Once the airlock has been cleared, turn off the outdoor tap and disconnect the hose. Refill the hot water system by turning on the mains water supply and reopen the stopcock valve. Afterward, close all the hot water taps and check the boiler pressure.

By following these methods with care and attention to detail, you can successfully fix a boiler airlock and restore normal functioning to your central heating system.

When to call an engineer

Sometimes, despite your best efforts, the boiler airlock problem persists. Engaging the services of a qualified heating engineer to diagnose the issue is crucial in such cases. In this section, we discuss when to call an engineer and some techniques professionals undertake to resolve airlock issues.

Identifying Persistent Problems

One major indication that you need to call a heating engineer is when repeated attempts to remove the airlock fail. 

Similarly, if cold spots on radiators or lack of hot water persist even after you have tried traditional DIY methods to fix the boiler airlock, seeking professional assistance becomes necessary.

Heating engineers not only provide expert diagnosis, but they can also offer advice on maintenance and other measures to prevent the recurrence of airlocks in your central heating system.

Furthermore, if there are other underlying issues contributing to the airlock that a non-professional may overlook, a qualified heating engineer is in a better position to detect and address them.

In some instances, the problem may not be related to an airlock at all. An experienced plumber or heating engineer can help you distinguish between airlock-related issues and other complications, such as faulty valves, broken pumps or aged pipework. Correctly identifying the root cause ensures effective rectification, saving you time, effort, and potentially additional costs in the long run.

In conclusion, you should call an engineer if you continue to experience boiler airlock issues despite your attempts to resolve them. A qualified professional can efficiently diagnose and rectify the problem while offering valuable advice for future maintenance to ensure your heating system operates smoothly.

New Boiler Installation

When considering a new boiler installation, it's essential to make an informed decision while bearing in mind the potential impact on the central heating system. In this section, we will discuss the key factors to consider before making a choice.

Taking the Right Decision

Selecting a new boiler is not an easy task, as various factors influence the performance of your central heating system. The following pointers may help you determine the best option for your home:

  • Gas boilers: These are the most common type of boilers used in the UK. They rely on natural gas to heat water, which is then circulated throughout your central heating system. Gas boilers are generally energy-efficient and produce fewer emissions compared to other types of boilers.

  • Excess water vapour: A byproduct of the combustion process in boilers is water vapour. In some cases, this excess water vapour may cause blockages in the system if not adequately managed. It is essential to ensure that your new boiler has mechanisms to effectively deal with this excess water vapour.

  • Cold water: Boilers require a supply of cold water to heat up and disperse throughout the central heating system. Ensure that the new boiler's water supply connection is accessible and can handle the required water pressure.

  • Blockage prevention: Boiler airlocks occur when air gets trapped in the system, leading to blockages and reduced efficiency. It is crucial that the new boiler you choose has features to prevent airlocks and facilitate easy maintenance.

By carefully considering these factors, you can make a confident and knowledgeable choice when selecting a new boiler for your home. It is vital to consult with a professional heating engineer to ensure the chosen boiler is suitable for your specific needs and central heating system, and to carry out a seamless installation.

Check out new boiler costs

Get a quote

Frequently Asked Questions

How do I get rid of the airlock in my boiler?

To remove an airlock from your boiler, follow these steps:

  1. Turn off your central heating and wait approximately 20 minutes for the system to cool down.
  2. Place a dry cloth or towel beneath the radiator you want to bleed, in case of water spillage.
  3. Slowly open the valve using a radiator key, turning it anti-clockwise.

Remember to always do this with caution and consult a professional if you're uncertain.

Will an airlock eventually clear itself?

An airlock rarely clears itself, and it's essential to address the issue promptly to avoid potential damage to your boiler or central heating system. To release trapped air, you must follow the steps mentioned above or consult a heating engineer for assistance.

What happens if air is trapped in a boiler?

When air is trapped in a boiler, it can cause a range of issues, including:

  • Inefficient heating, as air bubbles prevent proper circulation
  • Gurgling or bubbling noises from the boiler or pipes
  • Potential formation of rust due to oxygen in the trapped air

Addressing trapped air quickly can prevent further complications and potential damage to your central heating system.

Do combi boilers get air locks?

Combi boilers, like other types of boilers, can indeed get air locks. To handle an airlock in a combi boiler, first, turn off the main water supply, and then open all taps to drain water from the system. Consult a professional heating engineer if you're unsure about the process.

Can you bleed air out of a combi boiler?

Yes, you can bleed air out of a combi boiler. After turning off the main water supply and opening all taps, locate the radiator or boiler section with trapped air. Use a radiator key or valve to release the air, turning it slowly and carefully.

How do you purge the air from a combi boiler?

To purge air from a combi boiler, follow these steps:

  1. Turn off the boiler and allow it to cool down.
  2. Locate the airlock point - often near the pump or higher sections in the system.
  3. If your system has bleed valves, open them to release trapped air.

When purging air from your combi boiler, exercise caution and consult a professional heating engineer for assistance or advice if needed.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.