Expansion pot is a component which has to be installed inside the boiler in order to have the right functioning of the domestic heating. The water subject to treatments in order to quickly heating itself, which tends to increase its volume, so those who have built the boilers - in order to ensure a bigger safety - have installed inside the so-called expansion pots. This membrane device does nothing but absorbs the rise of the water volume, according to the increase of the temperature in a house heating plant. When the circuit has cold water, the membrane keeps it tight to the pot, without taking action. In order to ensure the maintenance of pressure when water is hot, the expansion pot activates the buffer which pushes the water out of the pot, putting it again inside the circuit.