Rewiring is disruptive and expensive, so it is worth being clear about what actually indicates a need for it rather than a need for a smaller repair.
The strongest indicator is the wiring type itself. Cloth-insulated conductors, rubber insulation that has gone brittle, or knob and tube runs are all associated with houses built before insulation standards changed. These materials degrade with age and heat, and once the insulation is failing there is no repair short of replacement.
The second indicator is a two-wire system with no ground. If every outlet in the house has two slots rather than three, the circuits have no equipment grounding conductor. Adapters that let three-prong plugs fit do not create a ground. They just remove the physical barrier.
Beyond the wiring type, the behaviour of the system tells you something.
Lights that dim noticeably when a large appliance starts suggest voltage drop, which can mean undersized conductors or loose connections. Occasional dimming when the air conditioning kicks in is normal. Consistent, obvious dimming across the house is not.
Warm switch plates or outlet covers are a serious sign. Wiring devices should be at room temperature. Warmth means resistance somewhere in the connection, and resistance means heat building where you cannot see it.
A persistent burning or fishy smell near a device is an immediate concern rather than a diagnostic one. Certain plastics used in wiring devices give off that odour as they overheat.
Frequent tripping across multiple circuits, rather than one, suggests the system as a whole is undersized for how the house is now used. A home wired for a refrigerator, a few lamps and a radio is being asked to run a very different set of loads today.
Not every one of these means full rewiring. A single warm outlet is usually one bad device. Dimming on one circuit is usually one connection. The case for rewiring builds when problems appear in several places at once, or when the wiring type itself is the issue.
A useful middle path in many homes is partial rewiring, replacing the runs that serve heavy loads and leaving lighting circuits in place, which spreads the cost over time.
A useful reference: heealthy.com
