Guide to header and expansion tanks

In the lofts of houses or business premises which are served by an older or traditionally designed heating system you’ll find two tanks. The smaller of the two is known as the header or expansion tank.

These tanks can come in slightly different shapes and sizes, but ultimately they all look roughly the same. The most common types are made of plastic, although some older versions can be made of asbestos.

 

What is a Header tank for?

Primarily the role of the header tank is to store the water from your heating system when it is heated up – it’s like an extension of the system, hence the name. But it also has other purposes:

• To store water when maintenance work is carried out.
• Allow air to escape from the heating circuit and fill the system up with water.
• Where you add inhibitor to your heating system. Inhibitor is a chemical that is designed to protect the system from corrosion.

Header tanks are to be found when the heating system is old or more traditionally designed – the modern, more efficient, central heating systems which are “pressurised” do not require a header or expansion tank at all. These systems are known as “sealed systems”.