Expert Advice & News



The impact of unwanted air within a heating system can be very damaging to the boiler and components and ultimately very costly for the homeowner, leading to serious inefficiencies and potential breakdowns.

Noisy radiators, radiator cold spots and lower heat outputs of radiators are all common symptoms related to air in the system, a short-term remedy, such as manual venting or a system flush my be sufficient, but most of the time these solutions will only hold the problems off for a while longer, they will inevitably surface again if the root cause isn’t addressed and the appropriate action taken.

In most cases, system problems can be traced back to the presence of microbubbles, these are tiny bubbles of air within the system water that need to be effectively and continuously removed for system efficiency and reliability to be maintained throughout the lifespan of the system.

Identifying the presence of air, and how it enters the system in the first place and how best to remove it isn't always straightforward, most people are familiar with the sludge (magnetite or iron oxide) that can clog up heating systems, but they are less likely to realise that air is causing these problems.

If radiators have cold spots, are heating up unevenly or have annoying clanging and banging noises, then pockets of air are more than likely slowing the flow and causing these problems.

A high volume of magnetite (sludge) is also a sign in itself that air is present. Its formation is only possible when oxygen and water combine, it then attacks the metals within the system, this includes the boilers heat exchanger and radiators, it will cause corrosion and block pipes, valves and pump impellers, so magnetite is actually a symptom of a much deeper problem.

There are three types of air within a heating system.

Free air, microbubbles and dissolved gases.

Free air is the air that can be found at the top of radiators and towel rails, dissolved gases are the bubbles that develop when the pressure is reduced within the system, and the smaller Microbubbles of air are so small in size that they are actually trapped within the water itself, but will be released from water as a result of changes in temperature.

Free air will enter a system in many ways, the most common being during the filling or refilling of a system when modifications and maintenance are carried out or if there is a leak in the pipework, or if there is incorrect system pressure.

The presence of air is completely unavoidable due to the microbubbles and dissolved gases that are naturally contained within water.

If microbubbles are left untreated, multiple issues will eventually occur. While at first seemingly harmless, if left for too long, microbubbles and air will make up a high proportion of the system water. This is very problematic for two reasons.

Firstly, the microbubbles are so small that they cannot form one larger pocket of air that could then be released by bleeding the radiators or fitting an automatic air vent.

Secondly, the microbubbles will eventually be reabsorbed as dissolved gases within system water. Most systems are made up of metals primarily consisting of iron. Just like when iron railings rust in the rain, the oxygen within water reacts with the iron to form iron oxide, otherwise known as magnetite. This magnetite debris will gradually build up within a system and lead to some serious component failures.

For a long time, it was widely believed in the industry that an AAV alone could overcome the issue of air within a heating system. However, while the valve is very useful during the filling or draining process, and for the ongoing release of free air, it does little to remove microbubbles.

The removal of microbubbles requires a deaerator – such as the SpiroVent RV2. This should be fitted on the flow pipe at the hottest point of a system, usually on the boiler flow pipe, as this is where microbubbles will form due to the increase in temperature. Air is then immediately removed before it has chance to compromise the system .

Air in a heating system can increase energy use by 6%, leading to unnecessarily high heating bills, as well as the risk of system and component breakdown, caused by magnetite contamination.

To avoid this, it is crucial that the long term benefits of deaeration are understood.

Unlike other methods, such as dirt separation or chemical inhibitor treatment, deaeration allows for prevention rather than dealing with the symptoms, ensuring the problems don’t come back.