How to clear an airlock in a central heating system?

central heating system installation

When it comes to maintaining an efficient central heating system, one common issue that homeowners often encounter is the dreaded airlock. An airlock can disrupt the flow of hot water and heating throughout your home, causing discomfort and frustration. 

In this comprehensive guide, we will walk you through the step-by-step process of clearing an airlock in your central heating system, ensuring that your home stays warm and cosy throughout the year.

Understanding the Problem

Before we delve into the solution, it’s essential to understand what an airlock in central heating systems is and why it occurs. An airlock happens when trapped air gets into the pipes of your heating system, preventing the flow of water. 

This can result from various factors, including a recent repair, maintenance work, or simply over time as air accumulates in the system.

Tools and Materials You’ll Need

Before you begin, make sure you have the following tools and materials at hand:

  • A towel or cloth
  • A radiator bleed key
  • A small container or cloth for catching water
  • A wrench

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Step 1: Turn Off Your Heating System

Begin by turning off your central heating system. Locate the thermostat and switch it off. This step is crucial to ensure your safety and avoid any accidental burns or scalds while working on the system.

Step 2: Identify the Problem Radiator ( trapped air)

In most cases, the radiator that’s affected by the airlock will be cooler than the others in your home. It’s essential to identify this radiator so that you can focus your efforts on it.

hot water system installation

Step 3: Prepare for Bleeding

Place a towel or cloth under the radiator to catch any water that may spill during the process. Next, use a radiator bleed key to open the bleed valve. 

You will find the bleed valve at the top of the radiator on one side.

Step 4: Bleeding the Radiator

Slowly turn the radiator bleed key anti-clockwise to open the valve. You’ll hear a hissing sound as the trapped air escapes. Keep turning the key until you see a small amount of water starting to drip out. 

This indicates that all the trapped air has been released.

Step 5: Tighten the Valve

Once all the air has been bled from the radiator, use the wrench to tighten the bleed valve in a clockwise direction. Be careful not to overtighten it, as this may damage the valve.

Step 6: Re-pressurize the System

Now that you’ve successfully removed the airlock ( radiator key) from the affected radiator, it’s time to re-pressurize your central heating system. 

Refer to your boiler’s manual for specific instructions on how to do this.

Step 7: Check for Leaks

After re-pressurizing the system, inspect the radiator and the surrounding pipes for any signs of leaks. If you notice any leaks, tighten the connections with a wrench or call a professional plumber for assistance.

our engineer removes the air from a radiotor through a radiator bleed valve

Identifying Excess Water Vapor

Water vapour often occurs when there is an issue with the water heating process. It can manifest as air trapped within the system, especially in the highest points such as the top floor radiators. 

This excess moisture can lead to cold radiators and cold spots in your home, indicating that the water flow is not as efficient as it should be.

Dealing with More Water Vapor

To resolve issues related to excess water vapour and airlocks, follow these steps:

  • Bleeding Radiators
  • Check Boiler Pressure
  • Use Corrosion Inhibitor Chemicals
  • Inspect for Leaks
  • Seek Professional Advice

Maintenance Tips for a Healthy Central Heating System

Now that you’ve learned how to clear an airlock in your central heating system, it’s essential to keep your system in excellent condition. 

Regular maintenance of your hot water system will not only prevent airlocks but also extend the lifespan of your heating system and improve its overall efficiency.

Schedule Annual Servicing

One of the best practices for maintaining a healthy central heating system is to schedule an annual servicing with a qualified heating engineer. During the service, they will inspect all components, clean the system, and make any necessary adjustments. 

This proactive approach can identify potential issues before they become major problems, saving you both time and money in the long run.

Bleed Your Radiators

As discussed earlier, bleeding your radiators is a simple yet effective way to prevent airlocks. Make it a habit to bleed your radiators at least once a year or whenever you notice cold spots on them. This will ensure that hot water circulates evenly, keeping your home warm and comfortable.

heating system repair by our engineer

Check for Leaks

Regularly inspect your central heating system for any signs of leaks. Leaking pipes or radiators can lead to not only reduced efficiency but also water damage to your home.

If you notice any leaks, address them promptly by tightening connections or calling a professional plumber.

Monitor Boiler Pressure

Your boiler’s pressure should be within the recommended range at all times. Refer to your boiler’s manual for specific pressure settings. If you’re uncertain, consult a heating engineer to check and adjust the pressure if necessary. 

Proper boiler pressure is essential for the efficient operation of your central heating system.

Install a Magnetic Filter

Consider installing a magnetic filter in your heating system. These filters help capture and remove debris and sludge from the water, preventing blockages in the pipes and radiators. A cleaner system is a more efficient system, reducing the risk of airlocks and improving overall performance.

Use Inhibitor Fluid

Adding an inhibitor fluid to your central heating system can protect it from corrosion and scale buildup. These additives help maintain water quality, preventing the accumulation of sludge and debris. Regularly checking and replenishing the inhibitor fluid will contribute to a healthier system.

Upgrade to a Smart Thermostat

Investing in a smart thermostat can offer several benefits for your central heating system. Smart thermostats allow you to control your heating remotely, create customized schedules, and optimize energy usage. By efficiently managing your heating, you can reduce wear and tear on the system and improve its longevity.


Clearing an airlock in your central heating system is a straightforward process that can save you time and money on unnecessary repairs. By following these steps, you can ensure that your home stays warm and comfortable throughout the colder months. Regular maintenance and bleeding of your radiators will help prevent airlocks and keep your central heating system running smoothly.

Remember, if you’re ever unsure about performing any of these steps, it’s always a good idea to consult a professional heating engineer to avoid any potential issues. With these guidelines in mind, you can keep your central heating system in top shape and enjoy a cosy and warm home all year round.

Excess water vapour can create issues within your central heating system. When excess water vapour is present, it can lead to airlock problems, causing disruptions in the flow of water and reducing the efficiency of your heating system. Here, we will discuss how to address excess water vapour and ensure that your system is working correctly

Quality Solutions from MML Plumbing

Reliable Engineers for Central Heating Airlock Fixes

Are you considering an upgrade to your central heating system? Opt for MML Plumbing’s expert boiler installation services. We guarantee a seamless and effective installation process, delivering a continuous flow of hot water and comfortable heating. For heating system problems contact our team to book a heating engineer. Reach out to us now for a booking!

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