I have an inflatable hot tub with a 1000W heater, a 50W filter pump, and a 600W air blower. The pump must be turned off when operating the blower. It is powered to a dedicated 20-amp fuse through a line that previously was hooked up to a small hot-water heater under the sink. The heater is not working properly (does not maintain 102--degree temp), and the blower trips the GFI after about 5 minutes. Is this an electrical problem? (Thanx in advance for any help!)

What does the manufacture say about the minimum power the whole bath tub need, do it come with separate plugs for the heater, pump or blower. Did you try it with a non gfi( don't get in the tub) It triped because it ,tub, was not properly wire? The temp is effect by the ambience temp, what outdoor temp does the manufacture recommend to use , to get the 102 F ?

A 20 amp dedicated line is more than enough for this unit. Is it new or used, if used why diod the owner get rid of it? Are you sure there isn't a problem with this unit because your power supply is sufficient.

Is this a 240v system or a 120v system I would think it is a 120v system since you stated the tub is inflatable, if so, the blow and pump motor may not work at the same time, this is save the amp draw on the system. Some of these inflatable tubs use something called a heat jackaett wrapped around the motor to produce heat. If the tub is and older tub you could have a calcified line slowing the heat exchange on no flow through the tube.
Do you have a LED indication on your top side indicitacting the temp? Who is the maf of the hot tub? Is the pump and blower separate from the tub?