Nonreturn valve

A nonreturn valve for an exhaust pipe of a combustion device, wherein the nonreturn valve has a tubular body which can be installed in a vertical portion of the exhaust pipe, a floating body, a valve seat disposed inside the tubular body for the floating body which is formed such that it is liftable from the valve seat by vertically upward steaming gas and a circumferential groove disposed radially inside the tubular body, defined by a radial inner circumferential wall portion, a radial outer circumferential wall portion and a bottom wall portion, wherein the radial inner circumferential wall portion and the bottom wall portion are formed internally within the tubular body, and wherein the radial inner circumferential wall portion is formed at least as a portion of a gas guiding channel extending toward the floating body with a mouth circumferential edge

• wherein,
• between the radial inner circumferential wall portion and the radial outer circumferential wall portion a tubularly formed buoyancy bodyforming the valve seat is disposed, which is formed to be movable in parallel to the radial inner circumferential wall portion between a buoyancy position in which the buoyancy body forms between itself and the mouth circumferential edge a circumferential passage gap connecting the circumferential groove to the gas guide channel and a blocking position closing the passage gap in an axial direction.