How to Clear an Airlock in A Hot Water System

Airlock is a common problem in hot water systems in UK homes, especially in older gravity-fed systems. It can also occur in hot-water systems during plumbing work. While it is not common in homes with a combi boiler, airlocks can still occur.

The problems a home may face when an airlock occurs include low hot pressure in hot water taps or no hot water flow from taps. In most cases, the users often experience spluttering water when a hot water tap is opened. All these are the indications of an airlock in the hot water pipework. There may be several reasons why an airlock occurs more frequently in older gravity-fed systems, but in most cases, it can be easily fixed without calling a professional plumber or a qualified boiler engineer.

Keep reading this article to understand what an airlock is, why it happens, how it can be fixed, and when to contact a professional plumber.

Understanding Hot Water System Airlock?

A hot water system comprises pipes, which transport hot water from the boiler to hot water taps and showers. When, for any reason, air becomes trapped inside these pipes, the flow of hot water is obstructed. As a result, hot water is prevented from flowing freely because the air trapped inside creates a blockage. When it happens, the pressure of hot water coming out of taps might be drastically reduced. While in some cases the hot tap may completely stop dispensing water, in others it may dispense hot water in the form of drops. In most cases, the hot tap starts spluttering.

Normally, an airlock occurs in homes that have a gravity-fed hot water system or where cold water comes through an overhead cold water storage tank, mostly located in the loft. In homes where a sealed heating system is installed, there is a remote chance of an airlock. But an airlock can also occur, irrespective of the water system, where plumbing work was carried out in recent days. The reason is that during plumbing work, air may enter the pipework and get trapped somewhere. Sometimes air may also be trapped in radiators.

Common Signs of An Airlock

If one or more of the following signs are noticed in a home, it usually indicates that an airlock has affected the hot water system:

·         Hot water taps are spluttering or spitting.

·         Cold water is running normally, but hot water is not working as usual.

·         Hot water is running very slowly, in the form of trickles.

·         Unusual gurgling sounds emerging from pipework.

·         The hot water problem started after a recent plumbing work.

·         The boiler is working properly, and radiators are heating up normally, but there is no or very slow hot water in taps and showers.

Common Reasons for the Occurrence of an Airlock

There might be several reasons for the occurrence of an airlock in a hot water system, but the most common causes are one or a combination of the following:

·         Draining The System – It is quite a frequent practice of the heating and boiler engineers to drain out the entire heating system to fix an ongoing issue. Sometimes, it may also become necessary to drain the system to conduct some work on the radiators only. In any such eventuality, it is highly likely that air may enter the system, causing an airlock.

·         Water Level in Overhead Cold Water Tank Is Low – This frequently happens in homes having an old heating system that requires an overhead cold water storage tank. This tank is mostly installed in the loft. The boiler receives cold water via this tank, in contrast to the modern boilers that get cold water directly from the mains supply line. If, for any reason, the water level reduces in the loft tank, air gets into the system, resulting in an airlock. In gravity-fed hot water systems, the hot water supply is dependent on water pressure from the overhead cold storage tank. In this case, air gets trapped in the hot water feed pipework, creating an airlock.   

·         System Has Leaks Somewhere – If any leaks develop anywhere in the entire hot water pipework, air gets trapped inside and accumulates at a certain point, causing blockage in the free flow of hot water.

·         Plumbing Work or New Installation Done – When any repair or maintenance work is conducted on the hot water pipework, there is every possibility of air entering the system, causing airlocks, after some time. It may also happen if a new pipe is installed to extend the hot water system.

·         Pump Is Changed or Upgraded – If any repair work is conducted on the pump, or when it is replaced or upgraded, it may result in trapping of air inside the system. 

Clearing An Airlock In A Hot Water System

Airlock can be cleared quite easily by the homeowners on their own, without calling a professional plumber, provided it is safe for them, and more importantly, they can access the system safely.

Here are some very useful and effective methods to clear an airlock:

1.     Hosepipe Method

This is the most effective and easiest way of clearing an airlock that every homeowner can do, especially for homes with gravity-fed hot water systems. It can be performed as follows:

·         Turn off the heating system.

·         Get a flexible hosepipe of an appropriate length that suits the distance between the affected tap and the cold-water tap, which gets water directly from the mains.

·         Attach one end of the hosepipe to the nearest cold-water tap, preferably in the kitchen, that gets water directly from the main supply line, rather than from a storage tank.

·         Attach the other end of the hosepipe to the hot water tap, which is affected by an airlock.

·         Both taps must be tightly connected; the connections must be tight enough to prevent water from leaking out of them.

·         First, fully turn on the hot water tap. Then turn on the cold-water tap. Doing so will allow cold water from the mains to enter with full pressure, forcing hot water from the hot tap backwards. During this process, the air trapped in the hot water pipe will be pushed back into the storage tank.

·         Let the cold water run into the hot water pipe for around 60 seconds.

·         Turn off both taps one after the other and then remove the hosepipe.

·         Test the hot water tap to see if it works normally.

If the problem persists, you may need to call a professional plumber to check and fix the issue.

2.     Gravity Flush Method

This method can be used as an alternate option to the hosepipe method. Just follow the steps as follows:

·         Turn off the heating system.

·         Turn on all hot water taps in the entire house.

·         First, open the hot taps on the ground floor and then on the upper floor.

·         Let the water drain from the hot water taps for 5 to 10 minutes, or longer if required.

·         The pressure created by gravity often works effectively to push trapped air out of the system.

3.     Lifting The Ball Valve of the Loft Tank Method

This method is effective for homes with a cold-water storage tank installed in the loft. The steps to follow are as follows:

·         Access the cold-water storage tank in the loft, if safe to do so.

·         Slowly lift the ball valve arm to increase water flow.

·         When more water enters the tank, the pressure temporarily increases.

·         When maximum water has entered the tank, open the hot water taps on the lower floor.

·         The additional pressure caused by more water in the tank may force the trapped air to escape from the system.

4.     If Airlock Occurs In A Home Having A Combi Boiler

Although there is a very low chance of an airlock in a heating system with a combi boiler, it may occasionally occur. This can be cleared by bleeding the radiators, which is quite easy and most homeowners are familiar with.

FAQs

1.     Can an airlock fix itself?

Yes, sometimes it gets removed automatically, without any manual effort. Small air bubbles often escape the system with the flow of water, but larger air pockets cannot be removed without a manual process.

2.     Can bleeding radiators clear a hot water airlock?

Bleeding of radiators removes air pockets from the heating system. Usually, it may not remove air from hot water pipes. But in any case, bleeding radiators is always recommended.

3.     How much time is required to clear an airlock?

With the hosepipe method, it may take less than 5 minutes, but the gravity flush typically takes 10 to 15 minutes.

4.     Can turning the boiler off clear the airlock?

The boiler is turned off for safety during the airlock removal procedure. But simply turning off a boiler does not clear an airlock.

5.     Does a power outage also cause an airlock?

Not necessarily, but if the system loses pressure or has recently been drained during maintenance, air may enter the pipework, causing an airlock.

Conclusion

An airlock in the hot water taps is quite common in homes with older boiler systems that require a cold-water storage tank rather than a direct mains supply. It normally does not happen in sealed systems, such as a combi boiler. An airlock is not dangerous, but it can be annoying when hot water suddenly stops coming from a hot tap or shower. Usually, an airlock can be cleared in just a few minutes, using the hosepipe method, without calling a professional plumber. However, regular maintenance, timely leak repairs, and maintaining the required water level in the loft tank can go a long way toward avoiding frequent airlocks.