If you suffer from air in central heating system problems, there can be several reason causing this.  Air can be caused by leaks in your heating system but may have entered the system during installation or otherwise could have gradually increased with the expansion and contraction of the system causing tiny air bubbles to be forced into the system.

Air entering the water heating system through leaks in the pipes can be the most troublesome cause of air in your radiators. These leaks can be caused by corrosion, damage to pipe joints, or a faulty radiator valve.

Why are my radiators full of air?

Most radiators will have a small amount of air in them, especially over time but even during the course of the heating system or radiator installation, some small bubbles of air may creep into the system. They can be created when your radiators are initially filled with water and a little air may remain in the system. 

Where does the air come from in my radiators?

They can be caused by leaks in your heating system, boiler or radiator.

Also, a natural side effect of the heating and cooling of water is expansion and contraction of the metal elements involved in the central heating system such as the boiler itself, the heating pipes around your property or the radiators themselves including the metal valves that the water has to pass through to get around the system, of course. 

This expansion and contraction can force tiny air bubbles into the heating system or radiators. These small bubbles rise to form larger pockets of trapped air which will displace the water at the top of your radiators, and since air doesn't conduct heat as well as water, you might notice these air pockets as cold areas at the top of your radiators. Due to the way air rises within the water, you may find that the radiators higher in your property suffer from the air in them the most.

What problems are caused by air in radiators?

A lot of air in a radiator can reduce the heat that the radiator can omit, and as a result, a lot of air in your radiator or overall central heating system will mean your home or business is not being heated as well as it should be, you may notice that even with the heating system on, your house is colder than it used to be when the central heating was first fitted.

Tiny bubbles do not cause any harm in the short term, however, you are still advised to remove them. Otherwise, you run the risk of the heating system oxidising over a longer period of time, this can lead to rust inside the central heating system which can create blockages in the central heating system, and also lead to further leaks or damage to the boiler.

If the air in your heating system is caused by leaks, then as well as the heating system reducing effectiveness, you may also have water leaking into your premises, either from the boiler itself, the radiator, from a valve or possibly even from a pipe, some of which may not be visible to you, as these may be embedded in your wall or floor of your property.

What are the symptoms of air in the central heating system?

You may notice over time that your radiators are not heating as well as they should, and particularly if the top of the radiator is colder than the bottom, then it’s likely you may have air in your radiators or air being passed through your central heating system.

Trapped air in your central heating system may also cause your radiators to make noises, like bubbling, gurgling and rattling. You may notice this particularly when the heating first turns on, but can happen at any time.

This may suggest that you need to bleed the radiators, and also look for the cause of the air entering your heating system.

Does air in my radiators cause low pressure?

If the air in your radiators was caused by a water leak and air creeping into the system as a result then the reduction of water in the system overall would be noticed as a reduction in pressure at the boiler pressure gauge.

Also if you bled your radiators recently to remove some air from the system, you may have also have lost some pressure. That's because, when you bleed a radiator, the air is released, which lowers the pressure in your overall central heating system and again this drop in pressure would be shown at the boiler gauge.

Air in the heating system does not cause a significant loss in pressure, however, as shown above, both the cause and effect of the air in the system definitely can.

Is air in a boiler dangerous?

Any sounds that indicate air in the central heating system and reaching the boiler, especially banging or whistling sounds should probably be looked at. They're likely to be caused by air or a build-up of material inside your central heating some of which you can take steps below to try and resolve. Usually, this is not a dangerous situation but if left unattended, your heating efficiency may be affected and could also lead to corrosion, and a build-up of this could cause an emergency boiler breakdown or expensive boiler repairs being required in future.

Central heating problems caused by air in the system

Air in the central heating system can cause a number of problems, including:

• noise, clanking or banging
• corrosion or rust
• lack of heating
• blockages

At the extreme and left untreated rust build up could clog up the central heating system leading to a failure of the boiler, or leaks to occur due to the pressure.

How do I get the air out of my radiator?

If you are wanting to try and resolve this yourself, then first turn off your heating, and ensure you have a valve key to loosen the valve at the top of your radiators. This is called “bleeding the radiators”.  You can also ask your plumber to do this as part of your boiler servicing.