In a method of monitoring an apparatus for temperature control media supply of a tool of an injection molding machine, the apparatus for temperature control media supply has a feed and a return, between which at least one temperature control conduit is arranged, wherein at least one through-flow sensor is arranged. At least one pressure drop is measured in the at least one temperature control conduit. At least one hydraulic resistance and/or at least one resistance change in the at least one temperature control conduit is calculated on the basis of at least one volume flow measured with the at least one through-flow sensor and on the basis of the at least one measured pressure drop, and the at least one hydraulic resistance and/or the at least one resistance change is visually represented.