Main Power Problems... Circuit Breaker Trips Digital Air
Existing and Previously working GFCI Protected Installation;
Self-Contained/Portable Spa 
Breaker Trips Immediately
This problem can be a bit of a pain to deal with sometimes, and requires a little time and back and forth trips to the circuit breaker to reset it.
220 Volt Spa Installation
1.  First remove or turn off power at the remote disconnect box at the spa. If your GFCI breaker installation is contained in the remote disconnect box, then skip this step.  Turn power on at the breaker.  If it doesn't trip off line, then the assumption at this point is that there is a fault beyond the disconnect box.  If the breaker still trips immediately, then there's a problem somewhere between the GFCI and the disconnect box.  Most likely causes are:
  • Water/Moisture in the disconnect box.
  • Bugs rewired your GFCI for you.  Double check it. Go
  • Defective GFCI.
2.  If there's a possibility that any part of the spa control box under the spa skirt has gotten wet, either through condensation, rain leaks, or spa water spillover, then this is your most likely culprit.  It only takes a bazillionth of a drop of water in the wrong place to cause a gfci to trip.  Either let the spa sit for a day or so to dry out, or use some other method of drying the inside and outside of the spa control box, paying particular attention to any fuse holder that is riveted to the side of the case (I spent two hours finding one of these hidden wet spots once, the rivet allowed the water to penetrate onto a small fuse-holder from the outside of the aluminum box!). 

A hair dryer can work well in this instance, but be sure that you use one that has a GFCI attached to the power cord to protect you from electrical shock.

3.  The next best alternative is to disconnect all devices attached to the spa control pack.  Pumps, blowers, ozonator, circulation pump, anything that is plugged into the spa pack.

  • If the GFCI doesn't trip, GOOD!  Now shut off the power, re-attach each device and re-energize power each time you plug one in.  Recommend trying the Ozonator first, Circulation Pump, or Blower.  The offending device will cause the GFCI to trip when it is plugged in. 
  • If the heater is turned off, and the GFCI trips with ANY device plugged in, that is, simply pulling a load from the circuit causes the GFCI to trip off-line, then it's a sure bet that the GFCI is defective.
  • Digital/Electronic Control Only - If the GFCI trips with NOTHING plugged into the spa control pack, then you should be able to unplug the power transformer from the main circuit board.  Disconnect it, and re-energize the GFCI.  If the GFCI still trips, then you've probably got a problem with the wiring in the control pack, or there's moisture somewhere on the main power lines inside.  It's going to take some rather intense visual inspection to find this problem.  You can try to disconnect the lines going to the heater, but most digital/electronic spa controls will have a certain delay time prior to sending power to the heater, which pretty much negates this option, unless your heater has shorted, and has shorted the relays closed with it. 
  • Electro-mechanical/Air Control Only - Once it has been ascertained that the GFCI is still tripping with all external devices disconnected, then the most likely cause is going to be the heater element.  With the thermostat turned all the way down... (off), re-energize the spa pack and see what happens.  If the GFCI still trips, then you've probably got a problem with the wiring in the control pack, or there's moisture somewhere on the main power lines inside.  It's going to take some rather intense visual inspection to find this problem. 
  • If nothing else works - Try this link first, then try replacing the GFCI.  (NEVER BYPASS A GFCI!). 
110 Volt Spa Installation

Basically, the same troubleshooting procedures will apply for a 110 Volt installation as for a 220, however, most spas designed to run solely on 110 volts will usually have a low current GFCI installed as part of the plug in cable, or built into the spa control pack. 
 

If you have one of these types of GFCI's, or if your GFCI is the outlet on the side of the home, then troubleshooting is usually a little simpler, since resetting the GFCI is usually a quick thing to accomplish.  There is one thing to remember about an installation of this kind though, even if the GFCI is contained in a weatherproof housing, it is still subject to environmental forces that a circuit breaker panel GFCI won't be, and is more prone to failure over certain periods of time. 

It may be the only way around this particular problem, but if you've exhausted all avenues of troubleshooting and come up with no solutions, then replacing the GFCI is usually a good idea.  A 110 Volt GFCI exposed to the elements that is in excess of 5 years old is a good candidate for replacement anyway.  Be sure to use a good quality brand name, such as one made by Leviton (TM).