Tracing an RCD trip

An emergency call-out to a troublesome RCD which came our way today. Aluminium wiring, no CPC on lighting and a Class I fitting in the bathroom all on the naughty list, but the trip itself was quickly narrowed down to a fault with the combi boiler. This one was just filmed off-the-cuff while we were there as we had the camera with us for another job. Not very exciting I'm afraid, just sparkies doing straight sparkie stuff sober. An important update info for you as of 28/08/19; GasSafe have informed me that it's best not to remove a boiler cover unless the manufacturer instructions explicitly state that it can be taken off by the user. I see some threads arguing the point (sorry folks, I got no notifications for the back-and-forth going on in the comments, I've only just seen it all). I take that on board. My mistake was assuming that the cover was decorative rather than functional, but GasSafe advise always assume the latter unless you have specific manufacturer instructions to hand confirming otherwise. I also assumed the manufacturers would make the electrical connections accessible to... you know... an electrician, after all, it would be annoying to trace a fault to such an appliance and have to call out a gas engineer only for it to be down to an improper connection quickly fixed with a twiddle or three of a screwdriver, but there you go. The customer afterwards called in a repair man who seems to have done little more than swap out plug fuses and change the flex before giving up. Curiously, he left the old flex still tacked to the wall with bare wires at each end. She then got in a Worcester Bosch engineer who perhaps lacked an IR tester or didn't know how to use one as he apparently just part-swapped the hell out of it until it worked again. I would have preferred a little more method with my faultfinding personally. Anyway, I popped back there again and it now reports an IR of 120M Ohm from the plugtop, so it's all back in action. The client has also been advised to have the Class I bathroom fitting changed to Class II and have an updated electrical inspection (last undertaken in 2007). Sorry, camerawork's a bit all over the place.