The Aqua-Hot fuse is located on PCB #5, rear run box, lower left. It is a 25-amp fuse labelled Aqua-Hot.
Use caution as this PCB is always hot, even with the battery disconnects off.
-Scott
** Edit **
In addition to the main 25-amp fuse (rear run box), there are also fuses for each of the three Aqua-Hot multiplex switches (channels), Diesel, Electric & Pre-Heat. The multiplex modules and fuses are located in the multiplex closet.