Boiler expansion tank: role and utility

An essential element for the proper functioning of a boiler installation, its role is both to absorb the variation in the volume of water in the event of a change in temperature, but also to prevent wear and tear on the heating circuit by maintaining of constant pressure. Discover in this article the role and usefulness of the expansion tank, but also our advice for adopting the right actions during a breakdown.

What is the role of the expansion vessel?

Concretely, when your boiler is running, the water contained in the heating circuit expands causing a variation in the volume of water under the effect of temperature. To avoid the danger represented by this pressure, the expansion vessel absorbs the excess water, thus avoiding a depression during cooling. Whether you are in an apartment or in a house, it is necessary to have your boiler checked once a year by a professional. During his visit, he will make sure that there is enough air in the expansion tank. Maintaining your boiler is therefore essential to prevent a certain number of inconveniences.

Operation of the expansion tank

The expansion vessel in the shape of a sphere or a metal cylinder. It is made up of two sections separated by a waterproof membrane or a bladder. The connection to the water network is made from the top. The installation placed on the water return makes it possible to evacuate the overflow of water.

At the bottom of the expansion tank, a valve specially dedicated to inflating or re-inflating the gas envelope makes it possible to avoid overpressure and/or to manage the correct pressure depending on the boiler model and its installation.

The objective is to have a constant pressure guaranteeing a long-lasting installation.

In all cases, a professional must ensure the correct adjustment of various parameters in order to avoid any risk of failure. In particular, he will ensure, using a manometer, that the pressure indicated in bar is sufficient. This annual maintenance is essential to prevent serious damage such as corrosion or the rupture of welds.

What are the different types of expansion tank?

There are different models. Open or closed expansion vessels, at constant or variable pressure. The most widespread are closed expansion tanks with variable pressure. They have either a membrane or a bladder. For both, the base part of the expansion vessel is filled with the excess volume of water in the circuit while the upper part is filled with compressed air.

The arrival of water in the vase pushes the air part which compresses, absorbing the overflow of pressure. Thus, the pressure remains stable. Similarly, the expansion tank will prevent depression when cooling the water.

Older boiler installations are equipped with open or closed expansion vessels at constant pressure. These models are not recommended today.

Systems with an open model have a direct impact on the corrosion of materials, whereas closed installations at constant pressure use a valve to evacuate excess water.

How to react when your expansion tank breaks down?

Apart from adjusting the pressure and draining the condensation water, there is no other maintenance to be planned for the expansion vessel. On the other hand, it is necessary to call a professional quickly when it shows signs of malfunction. But how to detect these signals?

Detect the failure of the expansion tank

Generally, when the water expands and the pressure increases, the boiler goes into safety. Before that, several indicators can warn of an upcoming breakdown, such as a frequent and regular drop in pressure or even the display of an error on your boiler.

For the oldest boilers, these features do not exist, they release small quantities of excess water through a safety valve.

At the slightest sign, it is best to approach your installer for an intervention. You can also try to inflate your expansion tank by yourself. For this, you will need to bring the necessary equipment (compressor, pressure gauge, etc.). Be careful though, a deflated expansion tank is just as dangerous as one that is overinflated. Note that the ideal pressure is between 0.8 and 1.5 bar.

Invest in an expansion tank

An expansion vessel has a lifespan of around 7 years (this varies depending on the model). When it is defective (sealing problem, water pressure variation, boiler safety), it leads to the formation of limescale and mud deposits. This results in a capacity to heat that is less efficient and consumes more energy.

In the majority of cases, faults are easily repairable. It is usually enough to adjust the pressure or drain the expansion tank to get the system working again. But in the case of a water leak, this is equivalent to a membrane or a bladder that is too worn or punctured. In this case, you will have no choice but to replace the defective vase.

If you must invest in a new boiler installationthe best thing is to compete and compare prices for an equivalent service.

Request quotes directly or online from various boiler installers.
The price varies according to the capacity and inflation pressure of the expansion tank. For this, the contractors will establish their quotes taking into account the place of installation and the power of the boiler.

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