Repair is often reasonable when the tank is sound and the problem is limited to a serviceable component, such as an element, thermostat, igniter, thermocouple, flame sensor, drain valve, or certain controls. The part must be available, and the rest of the heater should be in suitable condition.
Replacement becomes the stronger choice when the tank body is leaking, corrosion is extensive, repairs are recurring, or the cost of restoring an older unit is high relative to its remaining useful life. A leaking storage tank cannot be made dependable by replacing an external valve if water is escaping through the tank shell. Tankless units require a different assessment because scale, flow sensors, igniters, heat exchangers, and error codes affect the decision.
Frisco Water Heaters explains both paths when both are viable. The recommendation should account for the failure, equipment condition, installation access, fuel type, and expected repair cost. It should not be based on the symptom alone.