We have a LG Dishwasher. The first time it worked perfectly. The second time the machine started with the cycle and the tripped the power. What is the problem?

SOURCE: dishwasher is tripping off our safety switch

It depends on what kind of test he was doing. He was probably checking the amp draw which checks how much power the whole machine was pulling. This would be the way to check the problem you have as long as he checked it with everything running, motor, heater,..etc. If you find the amp draw to be too high, then you go to individual components.

SOURCE: BOSCH DISHWASHER Loss of power

check fuse in plug top,if its not that it could be door switch 30 years repairing. Close Ire....

SOURCE: SMEG DWI410 TRIPS CIRCUIT LATE IN WASHING CYCLE

just possibly
take the kick panel off. On some smeg, there is a small suppressor capacitor on the lhs tucked in the wiring. this breaks down. snip it off - no need to replace

SOURCE: Kenmore Elite wont power on

Door switch. If the washer thinks the door is open, it won't run.

SOURCE: Ariston Dishwasher LI 675 DUO

1) Ensure the dishwasher is turned off.
2) (may not apply) Turn the plastic blue lever located under the sink to the vertical position (this opens the valve, so water can go into the dishwasher)
3) Pour powder indo the dishwasher
4) Turn the dishwasher controller to the top position (the 12 o’clock position) – this is the eco-setting.
5) Press the on/power button on the dishwasher, so that it now turned on (a light will display)
6) Move the dishwasher controller to the “R” position (it’s on the very left), and leave it there a second or two.
7) Move the dishwasher controller back to the eco-setting (the 12 o’clock position