During the operation of the hot runner system, heating rods and heating rings are set around the runner. Therefore, the whole runner from the nozzle outlet of the injection molding machine to the gate is at high temperature, and the plastic in the runner remains in the molten state all the time. Even after shutdown, there is no need to open the runner to take out the molten material, as long as it is heated to the required temperature at the next startup. So how to maintain the hot runner during operation and after shutdown?