How to Fix Airlocks in Heating Systems

A warm home shouldn’t feel like a patchwork of hot and cold zones. But when airlocks in heating system setups take hold, that’s exactly what happens—radiators fail, heat stalls, and your system starts working harder for less comfort. 

It’s inefficient. It’s frustrating. And left unresolved, it can quietly drive up energy costs.

An airlock is simply trapped air preventing hot water from circulating properly through your heating system. If left unresolved, airlocks in heating system components can gradually reduce overall efficiency and increase energy usage.

This guide walks you through recognising airlocks, how to fix it, and when to call a professional.

Related: Uneven Heating in Rooms Explained

Common Signs You Have an Airlock in Your Heating System

A heating system not working properly is often the first red flag that trapped air may be disrupting circulation.

While the symptoms can sometimes resemble other heating issues, there are a few telltale signs that point specifically to trapped air.

Cold Radiators Despite Heating Being On

You turn the heating on. The boiler is running. But one or more radiators stay stubbornly cold. 

In many cases, the issue isn’t the entire radiator—it’s just part of it. Run your hand across the surface. If the bottom is warm while the top remains cold, trapped air is blocking the flow of hot water. The air rises and sits at the top, forming a barrier that prevents proper circulation.

This uneven heating often affects radiators on upper floors first, where air naturally accumulates. It’s one of the clearest indicators that you’re dealing with airlocks in heating systems rather than a mechanical failure.

Gurgling or Bubbling Noises

Gurgling, bubbling, or faint knocking sounds coming from your pipes or radiators are strong indicators of air trapped within the system.

These noises occur when water tries to move around pockets of air. Instead of flowing smoothly, it becomes turbulent. You’ll often notice these sounds most when the heating first kicks in, as the system begins pushing water through partially blocked pathways.

Related: What is that Strange Boiler Gurgling Noise When Heating Up?

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What Causes Airlocks in Central Heating Systems?

Airlocks are usually the result of common system interactions. Understanding the cause is what prevents repeat problems.

Trapped Air During Refilling

One of the most frequent causes of airlocks is introducing air into the system during refilling. This often happens after draining radiators, performing maintenance, or replacing components.

When water is reintroduced too quickly or without proper bleeding, air becomes trapped inside the pipes or radiators. That trapped air doesn’t always escape on its own. Instead, it settles into pockets that disrupt circulation.

Even small DIY tasks can trigger this if the system isn’t handled carefully. 

Low Water Pressure Issues

Pressure is what keeps your heating system moving—literally. 

When boiler pressure drops below the recommended range, water struggles to circulate effectively. That sluggish movement creates the perfect environment for air pockets to form and remain trapped.

Low pressure doesn’t just contribute to airlocks; it can also make them harder to remove. Check your boiler’s pressure gauge regularly. Most systems operate efficiently within a specific range, typically around 1 to 1.5 bar when cold.

Step-by-Step Guide to Fixing Airlocks

You can fix airlocks in heating systems by yourself if you do it carefully. Take your time. Follow the process. Remember that when it comes to your heating system, small details matter.

Bleeding Your Radiators Safely

• Before doing anything, switch off your heating system and allow it to cool. This reduces pressure and prevents burns.
• Locate the bleed valve at the top corner of the radiator. Using a radiator key, slowly turn the valve anticlockwise. You’ll hear a sharp hissing sound—that’s the trapped air escaping. It’s a good sign.
• Hold a cloth or container beneath the valve, because once the air is released, water will begin to trickle out. 
• As soon as the flow becomes steady and consistent, close the valve firmly by turning it clockwise again. Don’t overtighten—just secure it.

Repeat this process for any affected radiators. Once done, return to your boiler and check the pressure. 

Bleeding radiators often reduces system pressure slightly, so you may need to top it back up to maintain optimal performance.

Related: How to Bleed a Radiator the Easy Way

Using a Hose Method for Stubborn Airlocks

Some airlocks are more persistent. When bleeding alone doesn’t resolve the issue, a more forceful approach may be needed.

The hose method works by using mains water pressure to push trapped air through the system. This involves connecting a hose between a functioning radiator and the affected one, effectively forcing water through and dislodging the airlock.

It’s effective—but not without risk. Incorrect setup can lead to leaks, water damage, or unnecessary strain on your system. You need to ensure all connections are secure and that you fully understand how your system is configured before attempting this.

When to Call Our Team at Rowlen Boiler Services

There’s a clear line between a manageable DIY fix and a problem that needs professional intervention. 

If you’ve bled your radiators and the problem persists, something deeper may be at play. The same goes for recurring airlocks—if they keep coming back, it’s not just trapped air. It’s a system imbalance that needs diagnosing.

Frequent drops in boiler pressure, multiple radiators failing at once, or ongoing noises that don’t resolve are all signs that the issue extends beyond a simple fix.

At Rowlen Boiler Services, our experienced team can quickly diagnose and resolve even the most stubborn heating issues. Whether it’s a persistent airlock or a more complex system fault, we’re here to ensure your home stays warm, efficient, and problem-free.

If you’re unsure or want peace of mind, don’t hesitate to reach out—getting professional support early can save you time, stress, and costly repairs down the line.

Contact us today!