On another forum about hot tubs I belong to I’m helping a member with an intermittent GFCI fault. It happens once or twice a month. He has been trying to run it down for a while and being intermittent it is hard to fine as everything tests fine. The water heater 240V is often the problem as they develop weeping between power and the outer tube. Heater tests correct and heats water. With a multi-meter you measure zero ohms between tube and element. I told him he needs to put a megger on it with 500-1000 volts to look for insulation breakdown. The question is can he do this in place with water in the tube? I would think yes because the water would be acting to bridge and help the insulation failure and the extra voltage over 240V might cause the fault as it is borderline. I’m not sure of all the specifics and I’m not a pro. If anyone can offer an opinion it would be great. Thanks.