The GFI trips right as you flip it, the spa pack makes a click within that micro second. With the .3 amp fuse removed the GFI stays on but the spa pack does nothing. No readout from the top panel and after the normal prime time it does not kick on. So this fuse is needed for the M7 computer I would guess. It has no flow switch just two heat sensors on top of the heater, blocked in by the spa pack case. Just one led light and that is a foot above the pack. But that light was disconnected and the GFI still trips. I also am thinking it is this transformer the trouble shooting talks about, but do not know how to tell.