A well-functioning central heating system is key to keeping your home warm and comfortable. However, an air lock can disrupt the system’s efficiency, causing uneven heating or even preventing it from working altogether. The good news? Clearing an air lock is a straightforward process that can often be resolved without professional help.

This guide will explain what an air lock is, how to identify it, and the steps you can take to restore your system to full working order.

What Is an Air Lock in a Heating System?

An air lock occurs when air becomes trapped in the pipes or radiators of your central heating system, blocking the flow of water. This disruption can prevent the system from heating your home effectively.

Air locks are typically caused by air entering the system during maintenance or from small leaks in the pipes. While they’re a common issue, addressing them promptly is essential to prevent long-term damage or inefficiency.

If you’re uncertain what type of heating system you currently have (or what type would be best suited for a building project) read our guide on how to choose a heating system.

Signs of an Air Lock

Recognising the symptoms of an air lock can help you diagnose and resolve the issue quickly. Here are the most common signs:

Radiators Not Heating Up Properly

If one or more radiators in your home remain cold or only heat partially, it could be due to trapped air preventing hot water from circulating.

Unusual Noises from Pipes or Radiators

Banging, gurgling, or hissing sounds from your radiators or pipes are strong indicators of an air lock. These noises occur as air pockets interfere with the water flow.

Inconsistent Water Flow in the System

An air lock can cause uneven water flow, resulting in some parts of the system working while others don’t. This often leads to inconsistent heating throughout your home.

Heating System Fails to Start Properly

If your boiler or central heating system struggles to start or shuts down frequently, an air lock may be the underlying issue.

Tools and Materials Needed

Before attempting to clear an air lock, gather the following tools and materials:

• A radiator key
• Towels or cloths to catch water
• A small container to collect water from the radiator
• Adjustable wrench or screwdriver (if needed for pipe adjustments)

Having these items ready will make the process smoother and less messy.

How to Clear an Air Lock in a Central Heating System

Clearing an air lock requires careful attention to detail. Here are four effective methods to resolve the issue:

Method 1: Bleeding the Radiators

1. Turn Off the Heating System: Ensure the system is off and has cooled down to avoid burns.
2. Locate the Bleed Valve: Use a radiator key to open the bleed valve, usually located at the top of the radiator.
3. Release the Air: Turn the key counterclockwise to release trapped air. You’ll hear a hissing sound as the air escapes.
4. Close the Valve: Once water starts dripping, close the valve tightly. Repeat this process for all affected radiators.

Method 2: Balancing the System

1. Adjust the Radiator Valves: Ensure all radiator valves are open to promote even water flow.
2. Check the System Pressure: If the pressure is too low, refill the system to the recommended level.
3. Run the Heating System: Turn the heating back on and monitor the radiators for even heating.

Method 3: Forcing Water Through the System

1. Identify the Affected Area: Locate the section of the system with the air lock.
2. Increase Water Pressure: Use the filling loop to temporarily increase the water pressure in the system.
3. Force Out the Air: This increased pressure can help push the trapped air out of the system.

Method 4: Checking the Pump

1. Inspect the Pump: Ensure the pump is functioning correctly and not blocked by air.
2. Vent the Pump: Many pumps have a bleed screw that allows you to release trapped air.

How to Prevent Air Locks in the Future

Preventing air locks requires regular maintenance and attention to detail. Here are some strategies to keep your system running smoothly:

Psst! For additional advice, check out our guide on how to properly maintain your central heating system.

Regular Maintenance

Schedule annual servicing for your central heating system. Professional maintenance can identify potential issues before they cause air locks or other problems.

Proper System Refilling

When refilling the system after maintenance, ensure it’s done slowly and correctly to avoid introducing air.

Upgrading Components

Consider upgrading to a more efficient system with modern components. Options like high-performance air to water heat pumps can reduce the risk of air-related issues while improving energy efficiency.

When to Call a Professional

While many air lock issues can be resolved at home, some situations may require professional assistance:

• If the problem persists after trying the methods above.
• If your boiler or pump shows signs of damage or malfunction.
• If you’re unsure about any part of the process.

Calling a qualified heating engineer ensures the issue is resolved safely and effectively, preventing further complications.

Final Thoughts

Clearing an air lock in your central heating system is a manageable task with the right tools and techniques. By understanding the signs, taking prompt action, and practising regular maintenance, you can keep your heating system running efficiently.

With a little care and attention, your heating system will stay in top condition, keeping your home warm and comfortable year-round.

About the Author

Kane Brock, a certified Gas Safe heating engineer at Mr Central Heating, has 15 years of experience in the plumbing and heating sector. He expertly supports and advises fellow plumbers and installers purchasing products while actively taking on installation projects. This dual role keeps him engaged in his craft and ensure he continues to provide relevant expertise and product know-how.