A blood treatment apparatus comprising: - a dialysis filter or a receptacle for a dialysis filter ; - a dialysis fluid supply line having a first connector for supplying dialysis fluid to the dialysis filter ; - a dialysate discharge line having a second connector for discharging dialysate from the dialysis filter ; - a blood leak sensor configured and arranged to detect blood in or on the dialysis filter , in the dialysis fluid supply line and/or in the dialysate discharge line , and configured to emit a blood leak signal (BLS) if blood is detected; - a short-circuit line for connecting the dialysis fluid supply line and, or with, the dialysate discharge line in fluid communication, the short-circuit line comprising hereto a third connector and a fourth connector intended to be respectively connected with one of the first and second connectors ; - a controller configured to receive the blood leak signal (BLS) and characterized in that the controller is further configured to emit a signal which, in cooperation with the blood treatment apparatus , performs one, or at least one step from the group consisting of: - issuing a warning to the user that a cleaning of the third and/or fourth connector/s is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s ; - preventing the usability of the blood treatment apparatus , until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s with the first and/or second connector/s ; when a blood leak signal (BLS) has been emitted and/or received. - a dialysis filter or a receptacle for a dialysis filter ; - a dialysis fluid supply line having a first connector for supplying dialysis fluid to the dialysis filter ; - a dialysate discharge line having a second connector for discharging dialysate from the dialysis filter ; - a blood leak sensor configured and arranged to detect blood in or on the dialysis filter , in the dialysis fluid supply line and/or in the dialysate discharge line , and configured to emit a blood leak signal (BLS) if blood is detected; - a short-circuit line for connecting the dialysis fluid supply line and, or with, the dialysate discharge line in fluid communication, the short-circuit line comprising hereto a third connector and a fourth connector intended to be respectively connected with one of the first and second connectors ; - a controller configured to receive the blood leak signal (BLS) and characterized in that the controller is further configured to emit a signal which, in cooperation with the blood treatment apparatus , performs one, or at least one step from the group consisting of: - issuing a warning to the user that a cleaning of the third and/or fourth connector/s is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s ; - preventing the usability of the blood treatment apparatus , until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s with the first and/or second connector/s ; when a blood leak signal (BLS) has been emitted and/or received. - issuing a warning to the user that a cleaning of the third and/or fourth connector/s is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s ; - preventing the usability of the blood treatment apparatus , until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s with the first and/or second connector/s ; <EOS>