Just a clarification: "Faulty" doesn't mean "not working". If a fan in your laptop is designed to work for three years, then a faulty fan could stop working after 18 months. That fan would have been faulty from day one; the fault isn't that it's not spinning and cooling your laptop, the fault is that it breaks too early.
Strictly speaking, that is a separate issue of durability and is not subject to the same time constraints that applies to faults. If you buy a high value item, there is a certain expectation as to how long it should operate. These times are not enshrined within law but are subject to the legal minefield term of 'reasonable expectation'. If your laptop has parts (batteries!) that wear out before they are expected to then you are automatically entitled to a replacement, repair or refund without having to establish a fault at manufacture.
A fault would be harder to detect - more like poor wiring in the psu or a faulty capacitor leading to mainboard failure.