this is gonna be lenghty.... bear with me.
its a blue ridge air control timer pack , no circuit boards , just relays
i got a call the other day and man said his spa was tripping about every 3 days, so i go out and look at it and of course it looks ok and doesn't trip. he unplugged the ozonator and replaced the motor and heater element sometime back. at some time it had got very hot on the terminal block because it was melted and he just wire nutted 1 of the hot leads together instead of using terminal block and said it had worked fine for a few years that way. so i unhook the leads from the heater element and leave that way for a week or more and it never trips. so so i put on a new flow through heater and he also wanted a new ozonator which i put on. soon as i turn the heater on from topside control knob it trips instantly. heater seems to be good (11.2 ohms and continuity through elements but not from element to ground) and i can hear the contactor working. i put on another new heater just to be sure. same thing happens so i call blue ridge tech support and and describe all this and they recomended a new topside control which i installed and same problem. now there out of ideas and said good luck. so thinking the only thing left between topside and heater is the contactor so i replaced it and it ran fine for several minutes. so i reinstalled the old topside control because i didn't think it was faulty anyway. and it ran for 5 hours and tripped the breaker again. so i'm thinking that maybe this most recent trip was from the original problem. and the bad contactor was just bad luck that happened to happen in the midst of me trying to figure out the original problem. now i'm thinking high limit switch on my next try. any suggestions?

he has also installed a new 50 amp gfci

You didn't say if the GFCI was installed before or after all of this was going on.

What I would do is check the temperature of the GFCI Breaker when it trips.

If it's warm, there's your problem. Wiring at the GFI isn't tight enough. (This is what happened with the terminal block inside the controller - loose connections caused it to melt. http://spasupport.com/electrical/main/burnedwires.html

If not, then I'd proceed this way....
1. Power off.
2. Measure from RED (L2) to GROUND at the Control Box, with ohms on HIGHEST Setting (>200K). You should get almost no response.
3. Measure from Black (L1) to Ground. Same thing.
Depending on the brand of gfi, you may read the same thing from white (neutral) to ground in the control box. If you do get a reading, then disconnect the neutral power line coming into the spa pack, and check between the spa pack neutral and ground. You should get a reading of infinity.
4. Do a similar check between the heater terminals and ground. If you read ANY continuity between the terminals and ground, then you've got some defective heater elements, (possibly been manhandled or bounced around in the back of a truck for a while?). Note this check needs to be accomplished with the element immersed in water, and preferably sometime soon after the breaker has tripped.
5. If all above check good, then use an ac ammeter around the black (L1) and measure the amount of current draw.
Same with L2 then Neutral.

If you don't find any 'errant' readings, then try it with the o3 generator unplugged.

Lemme know what you find out.

wow! i had a awfull time trying to login and post for some reason.
but anyway thanks for the help. it turned out to be the thermostat. the gfci was replced before all of this. i replaced the entire topside and it hasn't tripped for a good while now. i ordered a new topside with digital readout from horizon but it wouldnt function properly. digital readout worked fine but idicator lights didn't work like they were supposed to. so ordered a new topside from blue ridge for that model tub and it works fine. the only thing is the tub wasn't originaly equipped with digital readout. and they dont make the face plate stickers without the digital readout window anymore. so everything works fine but no readout in the window. the customer is happy but i just hate to leave it like that.