A negative pressure wound therapy apparatus comprising: a negative pressure source configured to provide negative pressure via a fluid flow path to a dressing placed over a wound to create a seal over the wound; a pressure sensor configured to measure pressure in the fluid flow path; and a controller configured to, in response to a request to initiate or restart application of negative pressure: operate the negative pressure source in a first mode; determine a change in pressure in the fluid flow path over a period of time based on a plurality of measurements by the pressure sensor over the period of time; in response to a determination that pressure in the fluid flow path is decreasing, operate the negative pressure source in a second mode in which the negative pressure source provides a greater amount of negative pressure than in the first mode; and in response to a determination that pressure in the fluid flow path is not decreasing, provide an indication of a first leak in the seal and wherein: the request to initiate or restart application of negative pressure is associated with a negative pressure set point to be established in the fluid flow path; operation of the negative pressure source in the first mode is insufficient to reduce pressure in the fluid flow path to establish the negative pressure set point; and operation of the negative pressure source in the second mode is sufficient to reduce pressure in fluid flow path to establish the negative pressure set point. a negative pressure source configured to provide negative pressure via a fluid flow path to a dressing placed over a wound to create a seal over the wound; a pressure sensor configured to measure pressure in the fluid flow path; and a controller configured to, in response to a request to initiate or restart application of negative pressure: operate the negative pressure source in a first mode; determine a change in pressure in the fluid flow path over a period of time based on a plurality of measurements by the pressure sensor over the period of time; in response to a determination that pressure in the fluid flow path is decreasing, operate the negative pressure source in a second mode in which the negative pressure source provides a greater amount of negative pressure than in the first mode; and in response to a determination that pressure in the fluid flow path is not decreasing, provide an indication of a first leak in the seal and wherein: the request to initiate or restart application of negative pressure is associated with a negative pressure set point to be established in the fluid flow path; operation of the negative pressure source in the first mode is insufficient to reduce pressure in the fluid flow path to establish the negative pressure set point; and operation of the negative pressure source in the second mode is sufficient to reduce pressure in fluid flow path to establish the negative pressure set point. operate the negative pressure source in a first mode; determine a change in pressure in the fluid flow path over a period of time based on a plurality of measurements by the pressure sensor over the period of time; in response to a determination that pressure in the fluid flow path is decreasing, operate the negative pressure source in a second mode in which the negative pressure source provides a greater amount of negative pressure than in the first mode; and in response to a determination that pressure in the fluid flow path is not decreasing, provide an indication of a first leak in the seal and wherein: the request to initiate or restart application of negative pressure is associated with a negative pressure set point to be established in the fluid flow path; operation of the negative pressure source in the first mode is insufficient to reduce pressure in the fluid flow path to establish the negative pressure set point; and operation of the negative pressure source in the second mode is sufficient to reduce pressure in fluid flow path to establish the negative pressure set point. the request to initiate or restart application of negative pressure is associated with a negative pressure set point to be established in the fluid flow path; operation of the negative pressure source in the first mode is insufficient to reduce pressure in the fluid flow path to establish the negative pressure set point; and operation of the negative pressure source in the second mode is sufficient to reduce pressure in fluid flow path to establish the negative pressure set point.