Clearing an Airlock in Water Pipes: How To Do It Yourself

Airlocks in your water pipes are a common plumbing problem.

Fortunately, there are simple ways to fix this yourself.

Consider calling a professional first! It’s always best to call out a heating engineer or plumber for water pipe problems. They will diagnose the problem correctly, which will reduce the chances of damage. However, if you need - or want to - clear an airlock, the below steps will guide you.

What causes an airlock in a hot water system?

An airlock happens when pocketed air becomes trapped inside your hot water pipes. This air blocks the flow of water, leading to spluttering taps or banging pipes.

The most common causes include:

• Recent plumbing work: Installations or repairs can let air directly into your system.
• Incomplete system draining: If you drain your pipes for maintenance and refill them too quickly, air pockets can form.
• A dry water tank: If your cold water storage tank runs dry, air is easily sucked down into your hot water cylinder pipework.

Read: Heating Engineer vs Plumber — Which One Do You Need?

Will an airlock clear itself?

In some cases, yes. A very minor air pocket might occasionally clear itself over time under normal mains water pressure. 

But more often than not, the answer is no.

If you leave an airlock unresolved, the trapped air can cause serious issues. 

And leaving it risks permanent damage to your central heating pump, shower pump, or boiler components.

How to resolve a toilet airlock

A toilet airlock usually shows up as an incredibly slow cistern refill. This happens when air blocks the low-pressure cold water pipe fed from your storage tank.

If your toilet is refilling very slowly, you can use the cross-over flush method (detailed in Option A) on a nearby tap. 

Forcing high-pressure mains cold water through the pipes will often fix the issue by pushing the air bubble out of your shared pipework.

Read: Why Your Toilet Is Not Flushing (& How to Fix It)

Look beyond the pipes: Other issues to consider

Air bubbles can also get into radiators. If so, bleeding your radiators is the correct fix.

You must remember to turn your radiators off before doing this.

If it's cold weather, you should also consider whether you need to thaw your pipes.

Boilers are sophisticated pieces of machinery with many components. 

If you aren’t certain there’s an airlock in your water pipes, it’s worth considering whether basic boiler problems are causing your issues.

Option A: The Quick Fix - The Cross-Over Flush

This is a classic DIY plumbing method for clearing airlocks. It is specifically suited to a gravity-fed system (or tank-fed system), where water pressure is lower.

And it's best for fixing issues with a single tap.

Equipment needed

• A hose pipe at least 1 metre long
• Strong gaffer/duct tape or (preferably) two hose clamps (Jubilee clips)

Steps to take

Step 1: Check everything is on

Make sure your water is on/active. 

Ensure your main water stopcock is fully open and the small valves on the pipes under your sink are turned to the "on" position (the lever should line up with the pipe). 

Step 2: Connect taps 

Choose a sink with separate hot and cold taps. 

Connect the hot tap to the cold one using the hose pipe.

Step 3: Create a strong hose seal 

Secure the open ends of the hose tightly over the taps to ensure the water pressure won't blow the hose off. 

Hose clamps will give the strongest seal. 

If you are using duct tape, tie it tightly several times around. 

Step 4: Turn on the hot water 

Turn on the hot water tap (the one you have the hose tied to) fully.

Step 5: Turn on the cold tap (briefly) 

With the hot tap still running, slowly turn on the cold tap. 

Let it run (as the hot water tap is still running) for 30 - 60 seconds.

Listen closely for the sound of air being released. 

It should sound like a gurgling or sudden ‘burping’ noise.

Step 6: Turn off the taps

First, turn the cold (mains) tap off first, then the hot tap. 

(If the cold tap, i.e., mains tap, is still running into the hose and you close the hot tap, the mains water pressure has nowhere to go. 

So, it could  blow the hose off the tap and create a mess!).

Step 7: Repeat or finish 

Remove the hose from the taps. 

Check if another hot water tap is working in another sink in the house. 

If the water is spluttering, go back to step one: You may need to repeat this process at least 5 times.

If your hot water is working after that, and there is no spluttering, the process has worked. 

If not, consider Option B.

How to clear a combi boiler airlock

Airlocks inside a combi boilers are different from a simple tap issue. They can get trapped inside the boiler's internal heat exchanger, which is highly dangerous.

If your boiler has an airlock, do not turn it on.

Heating up the system while air is trapped inside risks dry-firing. This is when the internal metal components overheat instantly because there is no water to absorb the heat, which can crack components or cause a total boiler shutdown.

To clear a boiler airlock safely, you should use a complete system reset (described in Option B below). 

Always make sure your boiler is turned completely off before starting this process. Once you have successfully flushed the air out of all the taps, you can safely switch your boiler back on.

Read: Types of Boilers Explained: Combi, Conventional & System (Which Is Right for You?)

Option B: The Drastic Measure - A System Reset 

This is a process for clearing the entire hot water system, i.e. when multiple taps are showing signs of an airlock. 

 It should force out any air that’s trapped in your hot water system, allowing the hot water to flow out of your taps again. 

This is a riskier process than Option A. 

Before you start, turn off your boiler or immersion heater. Modern boilers use a "heat exchanger" to heat your water. 

If you turn the boiler on while air is still trapped inside, the metal can overheat instantly because there is no water to absorb the heat. 

This "dry-firing" can crack components or cause the boiler to shut down.

Step 1: Turn off your water supply 

Do this at the mains stopcock.

Step 2: Turn on every tap in the house 

Start at the top of your house and work your way downstairs.

Step 3: Let the water flow… 

Wait for the water to stop flowing out of the taps.

Step 5: Turn your taps almost off 

Adjust them until only a small amount of water can trickle out.

Step 6: Turn your water supply back on. 

Do it slowly! Doing it fast could create a 'water hammer' (a violent vibration that can loosen pipe joints). 

This is because a sudden rush of water into an empty system can hit air pockets.

Open the stopcock gradually to let the pressure build up gently.

Step 7: Turn on all taps halfway

Open each tap to a halfway point. 

You will likely hear a lot of noise as you do this, including: 

• Hissing
• Gurgling
• Spluttering
• Creaking. 

This is the air being pushed out by the new wall of water.

Keep the taps running until the flow is steady and the above sounds have stopped. 

This ensures the air is fully flushed out of the water pipes and - crucially - out of your boiler's internal heat exchanger. 

Step 8: Fully open up all the taps. 

Once the flow is steady, open them all the way to clear any final small airlocks. 

When you are happy the water is flowing perfectly, you can turn the taps off and switch your boiler back on.

If this doesn’t work (and you have tried option A), you’ll need to contact a professional to resolve the problem. 

It may be that debris  - rather than air - is blocking your pipes.

What to do after clearing an airlock

Releasing trapped air can cause a small pressure drop. 

To fix this, you may need to repressurise your boiler.