triping gfci

[morax]

let me start by saying hi to all.i have an old tub 110v1.5kwheater. my tub was working great for long time friday however my whole world changed.when i got in and pushed the button for high speed it tripped the gfci,i reset gfci it tripped instantly as soon as i turned on power.after letting it sit over night started no problem run on low speed no problem,high speed worked perfect like the past 4 to 5 hour later problem returns cool &repeat.the way it is wired is it goes to external gfci which has been replace with no resolve,however the spa pack has it own gfci which never trips.also if high is never selected never a problem run on low forever. anyone who can help or even give guidaince would be great

[In Canada eh]

morax,

     Let me start by first saying there are a couple of motor guys and a couple of electricians that frequent this site, if you wait patient you will get the correct answer.

     Here's my opinion,
         Your motor is drawing to many amps on high speed and thats causing a "over current" situation that in turn is causing your GFCI to trip.  Might be time for a new motor

[IDW]

9 ot of ten times a GFI trip is the heater. If you know what your doing you can disconect power to the heater and run the spa to see if the heater is the problem. You said the GFI in the house trips but not the one on the pak. GFI breakers do wear out especicially Federal pioneer.