Boiler Airlock: Causes And How To Fix It

Last Updated on January 28, 2025

When your boiler stops working as it should, it can disrupt your entire household, leaving you without hot water or heating, especially during colder months. One common issue faced by UK homeowners and landlords is a boiler airlock. 

In this guide, we’ll dive deep into what a boiler airlock is, the causes behind it, and how to fix it effectively.

What Is a Boiler Airlock?

A boiler airlock occurs when air becomes trapped in your central heating system, preventing water from circulating properly. This trapped air can block hot water from reaching radiators or taps, leaving parts of your system cold or completely unresponsive.

Signs of a Boiler Airlock

How can you tell if your boiler is suffering from a boiler airlock? Look out for the following symptoms:

• Radiators not heating up fully or staying cold.
• Hot water taps sputtering or producing little to no hot water.
• Unusual noises such as gurgling or banging coming from your boiler or pipes.

Common Causes of Boiler Airlocks

Understanding the causes of boiler airlocks can help prevent them in the future. Here are the most common reasons:

1. System Maintenance or Repairs
   When your heating system is drained for maintenance or repairs, air can enter the pipes, leading to an airlock.
2. Poor System Design
   Some older or improperly installed systems are more prone to airlocks due to inefficient pipe layouts.
3. Water Pressure Issues
   Low water pressure can make it easier for air to get trapped in the system.
4. Leaks in the System
   Small leaks in the pipework can allow air to enter and cause blockages over time.
5. Pump Failure
   A malfunctioning central heating pump may not circulate water effectively, increasing the likelihood of airlocks forming.

How to Fix a Boiler Airlock

If you’ve identified an airlock in your system, follow these steps to resolve it safely:

1. Bleed Your Radiators

Radiator bleeding is the most common method to remove trapped air:

• Turn off your central heating system.
• Locate the bleed valve on your radiator (usually at the top corner).
• Use a radiator key to turn the valve anti-clockwise slowly.
• Listen for a hissing sound as air escapes. Once water starts to trickle out, tighten the valve back.
• Repeat this for all radiators in your home.

2. Flush the System

If bleeding your radiators doesn’t solve the problem, a full system flush might be necessary:

• Turn off your boiler and allow the system to cool.
• Drain the system completely by opening the drain valve.
• Refill the system, ensuring there’s no trapped air in the process.

3. Adjust the Pump Settings

Sometimes, increasing the speed of your central heating pump can push the airlock through the system. Check your pump’s settings and consider running it at a higher speed temporarily.

4. Use a Hosepipe to Force Air Out

For severe airlocks, you may need to use a hosepipe:

• Turn off your boiler.
• Locate the affected tap or radiator and connect a hosepipe to it.
• Attach the other end of the hosepipe to a mains water tap.
• Turn on the mains tap to push water through the system, forcing the trapped air out.

5. Call a Professional

If you’re unable to resolve the airlock yourself or feel unsure about the process, it’s best to contact a qualified Gas Safe registered engineer. They’ll have the expertise and tools to diagnose and fix the problem efficiently.

How to Prevent Boiler Airlocks

Prevention is always better than cure. Here are some tips to keep your heating system airlock-free:

• Regularly bleed your radiators, especially after maintenance.
• Check for leaks in your pipework and have them repaired promptly.
• Maintain proper water pressure in your boiler system.
• Have your boiler serviced annually by a Gas Safe registered engineer.

When to Seek Professional Help

While minor airlocks can often be resolved with DIY methods, certain situations require professional intervention. Contact an expert if:

• The problem persists after trying the above steps.
• You suspect pump failure or significant leaks.
• Your boiler displays error codes indicating air circulation issues.

Conclusion

A boiler airlock can be a frustrating issue, but with the right knowledge and steps, it’s manageable. By understanding the causes, fixing the problem effectively, and taking preventative measures, you can ensure your heating system runs smoothly and efficiently. 

For UK homeowners and landlords, this not only ensures comfort but also helps maintain property value.

If you’re ever in doubt or need assistance, don’t hesitate to call a professional. A well-maintained boiler is essential for a warm and hassle-free home.