A detector for detecting the presence of a liquid comprising a probe sensitive to the presence of the liquid on contact with it, and a casing surrounding the probe comprising: a) an opening for receiving the liquid in the casing; b) an inlet distinct from the opening for the admission of a test liquid into the casing in contact with the probe, the placing of the test liquid in contact with the probe in the casing causing the presence of the test liquid to be detected if the probe operates correctly and causing no detection in the contrary case; and c) an outlet for the discharge of a portion of the test liquid from the casing after the test liquid has been placed in contact with the probe, the discharge being sufficient for the probe to no longer detect the test liquid remaining in the casing.