Disclosed are processes for a high temperature isomerization reaction converting (E)-1-chloro-3,3,3-trifluoropropene to (Z)-1-chloro-3,3,3-trifluoropropene. In certain aspects of the invention, such a process includes contacting a feed stream with a heated surface, where the feed stream includes (E)-1-chloro-3,3,3-trifluoropropene or mixture of (E)-1-chloro-3,3,3-trifluoropropene with (Z)-1-chloro-3,3,3-trifluoropropene. The resulting product stream includes (Z)-1-chloro-3,3,3-trifluoropropene and (E)-1-chloro-3,3,3-trifluoropropene, where the ratio of (Z) isomer to (E) isomer in the product stream is higher than the ratio feed stream. The (E) and (Z) isomers in the product stream may be separated from one another.