the fuel gas pressure in the combustion chamber heating rod 5 is supported in the center of body 6 using two spring diaphragms 1 2 which are deformable in the axial direction and which have the same spring stiffness thereby allowing heating rod 5 to move axially a reference element 3 e g a magnet is secured on heating rod 5 a displacement measuring element 4 e g an inductive coil is installed on body 6 an alternative to measuring displacement is to measure the deformation of the diaphragm as shown in fig2 one or more elastic sensing elements 4 such as strain gauges dms or capacitive sensors are installed on each of the two spring diaphragms 1 2 and send a signal to the control unit of a motor vehicle via a can bus via the displacement of the heating rod by the pressure present in the combustion chamber of the internal combustion engine if combustion pressure acts on the effective surface of heating rod 5 and combustion chamber side spring diaphragm 1 as shown in fig3 the heating rod moves relative to the combustion chamber and diaphragms 1 2 deform in the same direction measuring element 4 remains in its original position and reference element 7 moves with heating rod 5 the combustion pressure is deduced from the relative motion between measuring element 4 and reference element 7 fig4 shows a pressure measuring glow plug acted upon by fuel gas pressure with measurement of diaphragm deformation if combustion pressure acts on.