My spa will run for a day or two then trip the breaker. its a thermo spa model 1900
not sure of year, got it second hand. Have replaced the control box and heater.
Can someone tell me whats left? or is it that the motor is old and over heating
which causes it to trip? Thanks Any help will be appreciated

If it's not tripping the breaker within a few minutes of turning it on, it's probably not your hot tub causing the problem unless you've got a slow leak near some electrical equipment. Consider replacing the breaker and be sure that your neutral line is isolated all the way back to your main breaker panel.

Its seames like its been doing this since day one, the motor does make some noise that's why I thought
that the motor is over heating and throwing the out side breaker.
let me ask a stupid question, what do you mean by isolateing the neutral all the way back
to the main.

I'm assuming you have a 240v spa here...

You have a 4 wire connection: 2 hots, ground, and neutral. The neutral and ground are the same at the main panel, but should be on two different grounded hubs. Then, on the way to the spa, the ground connects to a grounding lug at every subpanel that is connected to the metal of the subpanel itself, whereas the neutral line is isolated all the way to the spa. If the ground is in contact with the neutral line between the main panel and the spa, it can cause problems with a GFCI.