Most electrical heaters, though not all, have two elements. One on the upper half of the tank and one on the lower half of the tank. These elements can be either high-watt or low-watt elements. Heaters are made so that the lower element works most of the time. The upper element comes on only when a large amount of water is used inside the tank. Elements rarely come on at the same time. Compartments on the side of the tank are where you can find the location of the elements. These compartments have thermostats although the upper element usually doesn't have a thermostat. The upper element is preset to be 120 degrees. It shuts off at 190 degrees if it ever reaches that high. There is a red reset button at the compartment which can turn the element back on if it overheats the circuit. If you only have one element it will be at the bottom of the tank and act like the upper element I just described. Thermostats work for many years on water heaters with usually no problems.

Sediment

Sediment build-up occurs very slowly, usually over several years. In an electric water heater, this can be detected by a bad sulphur odor or by lower electrical element burnout. The lower element is in the lower half of the water heater and is the apparatus that heats the water inside. Sediment inside the tank can pile up so high that the lower element is buried in it like an avalanche of hard snow. This causes it to overheat and burnout. Your showers and hot water will run out in half the time they used to if this happens.

There are two types of heating elements; a high-watt and a low-watt heating element. Which one you have inside the tank can cause sediment to produce faster or slower. The low-watt heating element is far superior. It has twice as much surface area and is not nearly as hot as a high-watt element. The lower heat still heats the water just as fast but produces far less sediment. If you ever replace a bad element, install a low-watt element in its place.

Elements are either bolted or screwed in to the water heater. They both come with a rubber or plastic water-tight gasket as well. If you remove the element for cleaning, install a new gasket as well, especially if the old one is hardened. If you have screw in heating elements, wrap the threads in teflon tape. Remember to turn off the power before working on elements. Immersion of the element in sediment can cause it to fail. Also, sediment can itself encrust around an element. Galvanic corrosion can cause an element to fail as well. It's rare that enough sediment would encrust itself around an element to cause it to burn up. Sediment usually flakes off an element naturally, but then the lower element can be buried. High-watt elements almost never encrust with sediment and make most sediment slough off to the bottom of the heater. A low-watt element may become encrusted with sediment though. I still recommend the low-watt density element for all its other benefits. If you have problems with elements burning out often, they may be cleaned. A toothbrush and some vinegar is all that is needed to clean elements. Galvanic corrosion can also occur between the copper sheath of the electrical element and its steel tank surroundings. This causes the joint to rust. The anode rod inside should protect against this problem. If you replace elements and they only last a few months, then the anode rod may be at fault and not the element.