GFCI tripping instantly after replacing.

[Jacuzzi Jim]

 My guess would be there is possibly a short somewhere.  I would let it run like you have been for a couple of days and see if it trips with the heater kicking off and on and same with the pumps, normal use.  Rare case maybe a bad breaker but doubt full.     Does it trip if you press the test btn?   

[Dr. Spa™ Ret.]

When the original GFCI tripped, did you just flip it to the on position, or did you forcefully push it towards the OFF position first, then to on (that's typically the correct way to reset a GFCI breaker).

Just to throw something into the mix...have you considered that the GFCI is actually working properly, and there's a short on the circuit board ;-)

[hottubdan]

Electricity can be dangerous.  Just the fact you are asking these questions makes me think you should hire a professional...or two.  You might need an electrician.  You might need a service tech.

Or,,,you might need a mortician. 

[Spa01]

Read the control box and see if that neutral is labeled on the lugs besides the red and black. If the neutral isnt hooked up right it can mess alot up. Only other thing i can say it try hooiing the ground to the breaker but that will prob just trip the system.

[Spa01]

Do you have an ozonator or any other accessories. Possibly on start up somthing is sending to ground. Your circulating pump and jet pump will all be grounded through the control box try disconnecting one at a time and see if one of them is possibly causing the trip