Any tips on steps to debug a panel-mounted GFCI breaker? I've got a pair of 50A GFCI breakers feeding my Nordic tub. In the past the breakers would trip for no apparent reason. Now it trips within about 2 minutes of being turned back on. But it does not immediately trip back off again.

I'm competent with all things electrical so I'm prepared to connect/disconnect/measure whatever's necessary.

The circuit comes from the breaker panel out to a box with a pair of fuses and a cut-off "plug". The GFCI does not trip if that plug is removed (which is no surprise) so at least the wiring up to that point is OK. Nor does it trip when the wiring to the tub's board is disconnected. So I'm guessing it's not the wiring from the breaker to the tub.

I should point out that when I went inside the Balboa controller box I discovered that one of the knockouts from the back of the electrical box had come loose and fallen "near" one of the heater terminals. It was not resting on it but I could see that at some point in the past it must've been close enough to have caused an arc. I've disconnected everything from the controller (heater, ozonator, pressure, pump motor) and the breaker still trips. That is, the controller board itself is connected but none of the circuits leading off it are connected. Turn it on for a few minutes and it'll trip. Turning the jets on/off, with the pump connected, seems to help it trip faster. I suppose it could be something to do with the controller board itself but it's not obvious.

These breakers are expensive so I'd really like to nail down if they're actually broken before I go replacing them. If/when I need to replace them, who's got them at a reasonable price?

Is the heater element still connected to the board? If so I would disconnect it and try again. If EVERYTHING is disconnected, it will be either the transformer, or the circuit board itself.

Turns out to be a combination of factors. A slight leak in the seals on the heater was intermittently causing a fault. Just enough would drip, apparently after recent rainstorms to make just enough of a puddle. Thus explaining it's near randomness. That and the contacts on the heater lugs were corroded and also seemed to cause it to trip. Thoroughly cleaning and snugly reconnecting all wiring seems to have cured it. It ran for over 8 hours, with several cyclings of the jets on/off and hasn't tripped once.

Although I haven't checked whether there were other power level issues. We've had some brownout periods off and on and I haven't correlated them against tub breaker tripping.