A capacitive priming sensor for a medical fluid delivery system is disclosed. In an example embodiment, a priming sensor includes a housing including a recessed section configured to accept a portion of a tube. The recessed section of the housing includes a first side including a first conductive plate and a member including a second conductive plate. The member is moveably connected to a second side of the recessed section for detecting insertion of the portion of the tube into the housing of the priming sensor. The recessed section also includes a third side opposing the first side. The third side includes a third conductive plate disposed across from a top portion of the first conductive plate, and a fourth conductive plate disposed across from a bottom portion of the first conductive plate. The priming sensor also includes capacitive sensors or detectors for measuring capacitances between the conductive plates.