Tracing an intermittent fault
An intermittent trip is the hardest kind of electrical fault to pin down and the easiest to be sold the wrong answer for. The circuit works, then it does not, and by the time anyone looks at it everything reads normal again.
The method is unglamorous: split the circuit, test each leg, and eliminate. Often it is a single accessory — a socket taking damp, a light fitting whose flex has chafed, a shower or immersion heater element starting to break down, or an appliance rather than the wiring at all. Older properties that have been extended in stages tend to hide the culprit in whichever part was added last.
What it usually is not is the consumer unit. A board that trips is protecting you from something further down the circuit, and swapping it leaves the fault exactly where it was. If a quote for an intermittent trip starts with a new board and no testing, it is worth asking what was tested and what the results were.