I have a 2001 Hot Springs Sovereign tub. It is setup for 115 volt, has the original watkins no fault heater. It has the factory setup gfci cord and waterproof box. I've had it since new and at about Christmas I noticed it was not heating up. I replaced the heater relay board (it has the IQ 2002 system) and everything worked fine until today. Now I noticed that the tub had no power. I flipped the inside circuit breaker in the house on and off (it was not tripped) and it went and stayed on. About 1/2 hour later or so I noticed it was off again. I repeated the steps above and then actual went in the tub for about an hour. The whole time the tub remained powered and I even occassionally used the jets. About 15 minutes or so after I was done, tub lost power again. Now the gfci just trips instantly. I removed the wires from the heater to the IQ unit and the tub had power again and the circulator pump kicked on. GFCI did not trip again. Do you think it's the heater? or could it still be the gfci or cord? Thanks in advance

If you removed the heater power wires and everything works again, you've kind of diagnosed your own problem...

Yes. It's the Heater.

When I disconnect the heater wires the spa jet pump doesn't work either.
Would this still indicate it's the heater and not something with the jet pump
(I don't believe so as this morning it powered up fine and the heater kicked on....but I'm betting since I've been at work it's off again, and while the heater is on, my hot tub is wired to not be able to have the jets go on at the same time) Do you think the heater might have been the cause of my original issue with the heater board failing as well?

What are the "power" and "ready" indicator lights doing at this point?

well the ready light wasn't green because the heater wasn't up to temp.
I don't remember what the power light was doing (I assume it was on though because the circulator pump was going with the heater disconnected) After sitting all night when I repowered back up with the heater connected, both the power and ready (I bumped down the temp until the light came on, just to see how far it dropped) lights were on
and in about 20 minutes the tub was getting hot like normal.

No, the heater is not the cause of the board failure.
Since the breaker never tripped, but re-setting it regained you power, it's a good bet the electronic heater-high limit tripped. Turning the breaker off, then oagain will reset the heater high limit.

Possible reasons for it tripping include dirty filter, circ pump beginning to fail, or a bad thermistor.

Keep an eye on the power light next time you "lose" power.

Sometimes when the circ pump fails and the heater subsequently overheats, turning the breaker off, then on again will not allow enough time for the heater to cool enough for the high limit to reset, and the spa will still have no power.

Keep a close eye on the circ pump flow.

Thanks for all your help. I replaced the heater and the thermistors.
Once I reset the heater by pressing the test button on my gfci, waiting
10 minutes and then hitting the reset button on the gfci, my tub was starting to heat and in a few hours was back to normal!!