A dialysis system is disclosed. The example dialysis system includes a housing, a pump actuator housed by the housing, a fluid pumping cassette coupled operably to the housing and including a flexible membrane covering a pump chamber, and a mechanically actuated piston head provided by the pump actuator and positioned to extend towards and away from the fluid pumping cassette. The fluid pumping cassette is positioned such that the flexible membrane of the fluid pumping cassette faces the piston head so that the piston head can push the flexible membrane into the pump chamber of the fluid pumping cassette to expel a fluid from the pump chamber. The example dialysis system also includes a controller programmed to perform a leak test by monitoring a sensed position of the mechanically actuated piston head while the mechanically actuated piston head applies a force to the flexible membrane of the fluid pumping cassette.