During the initial filling of the heating system, the network must be purged while cold. This first purging should be done from the lower floors to the upper ones, so that air trapped in the higher points of the installation is gradually removed.

The final (and any intermediate or subsequent) purging should be done with a warm network and low pressure, in order to reduce the solubility of air in the water, effectively separating the air from the water so we can remove as much air as possible from the network.

During the purging process, we should remove the trapped air from the network without removing water as much as possible, because removing water means that new water will enter from the system's filling point. This new water will contain new air that will also need to be removed.