I’ve found wiring to be one of the most fragile parts of my 3D printers. Fans can often fail where the wires are connected to the PCB, which can be particularly frustrating failure since there’s often limited clearance for soldering and most fans are welded together, making them difficult to disassemble. Fortunately, a bit of preventative reinforcement can significantly reduce the odds of a broken fan.
The fans usually break when the wires are attached to the circuit board, either the wire breaks or the solder pad comes off. Most fans come with a small plastic strain relief clip, but they’re usually not sufficient if the fans are installed in a way where the wires are moving continuously. Before installing any fan I always glue the wires to the fan housing so any movement or pulling of the wires doesn’t put any strain on the solder connection. Doing this when you first get the fan would be even better as it’s fairly easy to break the wires if you have a box of loose fans. I’ve been using Aquaseal* (a urethane wetsuit glue), but there are probably many options that would work just as well (maybe glue gun or shoo goo?).