A fume-discharge device for boilers is described which comprises a main duct (2) in which a first and a second tubular section (3, 4) for fume intake and exhaust, respectively, are defined, a third section (5) being interposed between the first and the second section (3, 4) and including a valve seat (6) having an opening (10) for communication between the first and second section, a shutter member (7) being provided for cooperation with the valve seat (6) and for being moved from and to a position of closing off the valve seat, in order to oppose the return of the fumes in the direction towards the first section (3), means for guiding the shutter being provided in the region of the valve seat (6) in order to guide, in a manner movable to a limited extent, the shutter (7) from and to the closing-off position by the action of the passage of the fumes in the duct (2), wherein the valve opening (10) is defined at the end of a cylindrical portion (9) of the third section (5), and the shutter (7) comprises a plurality of rod-shaped appendages (12) which rise in the same direction from the shutter (7) and which are capable of engaging inside the portion (9) in relative sliding contact with the cylindrical profile thereof for the axial guiding of the shutter (7) from and to the valve seat (6) coaxially with the opening.