The invention relates to a machine for descaling cells (3) of a cellular runoff body (2) used in an air-water exchanger, characterized in that it comprises at least one tool (6, 7) having an active tip (6a, 7a) and mounted on a frame (1) so as to be mobile between two positions in one direction common to all of the tools (6, 7) supported by the frame (1), the active tip (6a, 7a) of said tool being supported by the end of a rod (13) of a cylinder (11), the body (12) of which is mounted so as to be mobile relative to the frame (1) along the axis thereof, a piston (23) rigidly connected to the rod (13) and defining, in the body, a first chamber (26) which is constantly connected to a source of pressurized fluid and to a second chamber (27) through which the rod (13) passes, is in communication with the first chamber (26) as long as the rod (13) is at least partially retracted into the cylinder body (12) and insulated from the latter, and is connected to the exhaust when the rod (13) is in an end extension position outside the body (12).