Never take electrical safety risks by trying to look for faults yourself. Some safety precautions we obey are: turn off the main power at the unit / fuse box.
Types Of Fault We Find
Earth Fault, Tripping Circuit Breaker/RCD. Dead Short, Phase to Neutral/Phase to Phase, Correct Protective Device in place, Defective Components, Breakdown of Control Circuits, Reversed Polarity, Initial Faults on newly Installed work.
There are only a number of reasons why a circuit is going to stop working as it should. As an electrician becomes more advanced and discovers more of these faults they learn to know them very easily, and then they need only prove their hypothesis by checking the circuit successfully to reaffirm their initial assumptions. Repair is often easy once the fault is located.