Water heaters once installed can be forgotten about especially if they are in an attic. They sit there and quietly perform their function without much attention. We usually don’t check on them until there is trouble. Water heaters have a life expectancy of 7 to 12 years. One cannot predict with certainty when replacement will become necessary.
Some of the homes I have inspected have water heaters still working from the 1980s. We recommend changing them out at the 10 year mark as preventive maintenance. Manufactures recommend testing the water heater temperature and pressure relief valve routinely to ensure that waterways are clear and the device is free of corrosion deposits.
Manufacturers also strongly recommend that a qualified plumbing contractor remove the T&P valves over 3 years of age and inspect them for corrosion or sediment build up and proper condition. It has been our experience that valves, which have not been properly maintained or are in excess of 3 years of age do not reseat themselves or may later begin to leak.
The danger of a defective T&P valve is that water in a closed system (water heater tank) and under pressure has a much higher boiling point, which varies with pressure. When water heaters fail they can cause a lot of damage especially if they are in an attic. In addition to the explosion hazard described above, water heaters can release carbon monoxide.
If the sections of the water heater flue are improperly installed, they can become separated keeping the harmful carbon monoxide exhaust from terminating to the outside air. This can lead to possibly carbon monoxide entering into the living space posing a potential health threat. If you see the flue is disconnected a licensed plumber should be contracted immediately for evaluation and repair.
Hot water should be maintained at 120 degrees for hygiene and energy saving concerns. Anything over 120 degrees can be too hot for the skin and scalding could occur. The tank should be flushed once a year in an attempt to remove some of the build-up.