The average lifespan of a water heater is 8 to 12 years, notes Lowe's. Different factors, such as the way the unit was installed and maintained, affect the lifespan, either extending it or shortening it.
A water heater that is 10 years old and leaking or malfunctioning likely needs to be replaced, although some repairs are possible. Possible repairs include draining the tank to remove sediment, replacing a leaky pressure-relief valve, resetting the water heater's thermostat or tightening loose pipe fittings. Some things to consider when replacing a worn out unit include the energy efficiency rating of the new unit, the physical size of the unit, how many gallons it can heat in an hour and the gallons needed to accommodate a family's hot water needs.