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.