An apparatus and method for a hot runner injection molding system. The injection molding system has a plurality of melt conveying components defining a melt path from a melt source to a mold cavity and a mold housing. A force sensor or load cell is utilized between at least one melt conveying component of the system and the mold housing to measure a force generated due to thermal expansion of the melt conveying component during start-up and/or operation of the system and to provide an output to a receiving device. In an embodiment, once a sealing load or a predetermined preload force has been reached, an injection molding cycle may begin.