Replacing the power cord on a vacuum cleaner is crucial when you notice visible damage, such as frayed or exposed wires, cracks in the insulation, burn marks, or discoloration, as these issues can pose significant safety risks. Frequent electrical problems, like sporadic power loss or a loose plug, indicate poor connections that can lead to electric shocks or fire hazards due to electrical arcing. Additionally, old cords may become stiff or brittle, increasing the likelihood of cracking and exposing live wires. Such damaged or faulty cords not only compromise the vacuum's efficiency but also threaten to overheat, damage internal components, or cause fires. If you observe any of these signs, replacing the power cord should be a priority to ensure safe and effective operation of the vacuum cleaner.