Negative pressure therapy system for providing negative pressure for the medical negative pressure treatment of wounds on the human or animal body, comprising - a suction pump which generates negative pressure, - a suction line leading to the body, the suction line being subjected to negative pressure by the suction pump , - optionally a container for receiving bodily fluids, in particular from wound secretions suctioned out of a wound , - a pressure sensor for detecting the pressure in a pressure measuring line leading to the body or in the suction line or in the container or in the wound , - an electronic control device which controls the suction pump at least taking into account predefined and/or predefinable parameters and pressure values detected by the pressure sensor ; the electronic control device being designed to carry out a method comprising the following steps: detecting the pressure and activating the suction pump in order to achieve a predefined target negative pressure, and deactivating the suction pump when the target negative pressure is present, characterized in that , when the suction pump is activated, a check is carried out as to whether a pressure change rate toward increasing negative pressure remains below a predefined first threshold value S1 within a predefined first time span Δt1, and in that a check is carried out as to whether a negative pressure above a predefined second threshold value S2 is present, and, if both are true, the suction pump is stopped, and in that , when the suction pump is stopped, the pressure change rate toward decreasing negative pressure is determined, and in that a leak in the negative pressure therapy system is inferred if the pressure change rate is above a predefined third threshold value S3, and/or in that a blockage in the negative pressure therapy system is inferred if the pressure change rate is below a predefined fourth threshold value S4. - a suction pump which generates negative pressure, - a suction line leading to the body, the suction line being subjected to negative pressure by the suction pump , - optionally a container for receiving bodily fluids, in particular from wound secretions suctioned out of a wound , - a pressure sensor for detecting the pressure in a pressure measuring line leading to the body or in the suction line or in the container or in the wound , - an electronic control device which controls the suction pump at least taking into account predefined and/or predefinable parameters and pressure values detected by the pressure sensor ; the electronic control device being designed to carry out a method comprising the following steps: detecting the pressure and activating the suction pump in order to achieve a predefined target negative pressure, and deactivating the suction pump when the target negative pressure is present, characterized in that , when the suction pump is activated, a check is carried out as to whether a pressure change rate toward increasing negative pressure remains below a predefined first threshold value S1 within a predefined first time span Δt1, and in that a check is carried out as to whether a negative pressure above a predefined second threshold value S2 is present, and, if both are true, the suction pump is stopped, and in that , when the suction pump is stopped, the pressure change rate toward decreasing negative pressure is determined, and in that a leak in the negative pressure therapy system is inferred if the pressure change rate is above a predefined third threshold value S3, and/or in that a blockage in the negative pressure therapy system is inferred if the pressure change rate is below a predefined fourth threshold value S4. <EOS>