Why is everyone replace their water heaters...just drain it and replace the heater element.
The vast majority of water heater failures come from the Internal corrosion of the pressure vessel itself. Most of that corrosion comes from precipitate that collects at the bottom and other surfaces of the pressure vessel.
On single pass gas-fired fire tube water heaters, the vast majority of failures occur at fire tubes close to the lower tube sheet. Those failures are directly related to the amount of precipitate allowed to accumulate in the bottom of the water heater. The accumulation of precipitate inhibits proper heat transfer to the water in overheats and fatigues the tube. Internally, this destroys the'glass' lining in those style of water heaters And allows corrosion to occupy the cracks that will come from the fatigue of the lack of heat transfer.
And some failures can be due to leaks at either the supply or outlet attached to the pressure vessel.
The best way to extend the life of that style of water heater is to flush the sediments from it!
Although the initial outlet can be greater in purchase price and installation, the best bet on the market for the average home usage is the gas fired instant on demand and unlimited hot water style water heaters. They only heat the water when there is demand and there is far less water to heat at one time! The heating savings can recover the initial outlay in a relatively quick time.
The electric ones are more expensive to operate in the heating elements are a source of failure.
The gas fired are copper fined tubes with the water flowing in the inside and the fire on the outside. While going through the cycles of demand and non usage, the expansion and contraction of the copper tubing tends to not let the precipitate accumulate inside the tube.
Condensing water heaters are more efficient than non, but care needs To be taking it when installing the stack to properly deal with any condensation and proper air flow through the heater. Just through the natural combustion process, there will be a carbon buildup to some degree. Under heat and when the moisture hits the carbon it can form carbonic acid and that will quickly eat up the copper. When this style first came out I saw quite a bit of failures due to just this one thing.