Just moved a nordic tub that was running on 110volts to another home and now have it wired for 220 volts.My GFCI keeps tripping as soon as I turn it on. I tried to rewire it again for 110volts and it still trips. Put back to 220volts, tried unhooking eveything but the heater, but still keeps tripping. One thing I did not unhook is the heater and from reading on here am going to try that next. Does moving a tub 10 miles in the back of a U-haul really cause the heater to go bad?

Sometimes just draining the spa and the heater drys out can cause it to trip a breaker. Let us know if un hooking it cured your problem.

Disconnected the heater and it did not resolve the problem. Tried resistance test on the heater casing and posts/elements. No reading. Touching two posts I get a reading. So I'm assuming there is not a problem with the heater.

Disconnected wiring harness to pump/motor, thermostat, pressure switch, touchpad, and pulled 25A fuse labeled for pump. GFCI still trips.

This is a Nordic model spa with a SSPA-1 Power Spa Pack. Single 2-speed motor with electric touch pad control. A Gecko logo is on the inside of the power pack cover. The heater is approx 15" flow through. The spa was originally running on 110V with no problem. New wiring for 220V. Electrical wiring has tested fine up to tub. Attempted putting back to 110V. GFCI still trips.

Any other thoughts before replacing the power pack or calling service?

I would now say you could have the breaker hooked up wrong. The white curly wire from the GFI goes to the neutral bus, the white wire from the spa goes to the breaker. Most peaple get those two wrong.
Take a look at your wiring and let me know.

Thank you very much!! The white wires were hooked up incorrectly. Wow....if I could give you a rating. it would be all 10s. Thank you. Switched the wires around and everything started up. I was even surprised to not have a problem with the heater as many of the comments suggested.