. A new anode is compared to one that had been in use for many years.
The single most important factor in whether a water heater lives or dies is the condition of its sacrificial anode This is a rod made of magnesium or aluminum, that's wrapped around a steel core wire, and is screwed into the top of the tank. Physically connected to the steel of the tank, it creates an electrochemical reaction, similar to that of a battery, whereby the anode corrodes and the steel remains intact. When there's no sacrificial metal left on the anode, the tank rusts out.
All metals fall somewhere on the galvanic scale, and the "nobler" ones will remain intact while the lesser ones corrode. When steel and copper are together, the steel will corrode while the copper remains intact.
High on the list is forming a layer of insulation between the gas burner and the water. The sediment slows heat transfer and overheats the tank bottom. Overheating weakens the steel and can damage the glass lining, hastening the day when the tank will fail altogether. In the case of electrics, it can bury the lower element, causing it to burn out.
It also creates an anaerobic playground for corrosive bacteria.
In addition, it lowers the energy efficiency of the tank.
Sediment can drift into recirculating lines, jam open check valves, and cause the recirculating pump to stick until it burns out.
Finally, it causes noise, sometimes enough noise to annoy, or even frighten, people if the tank is inside a dwelling. The noise is caused by small amounts of water under the sediment layer turning to steam bubbles, which then collapse violently.
Rheem hot water heaters have a longer dip tube and thus this problem does not occur as quickly as with other hot water heaters.
There are also chemical applications for removing sediment. Some are dangerous, all are time-consuming.
Info from www.waterheaterrescue.com