on a hot water heater should the upper and lower thermostats be set the same?

they do not have to be set at the same temp but they can be set at the same temp....I usually set the lower one about 5 to 10 degrees higher than the upper one ...the way a heater works is like this, you use water the lower element comes on first as you use more water the bottom one shuts off and the top one turns on...when you quit using water the upper element stays on until the upper thermostat turns it off and turns the bottom element back on...the bottom element stays on until the lower thermostat turns it off...only the lower element will come on periodically to keep water temp at the thermostats setting until you start using water then the cycle repeats...bottom element then top element then back to bottom element...if you do not use a lot of hot water the top element might not even turn on.

Water Heater Thermostat Settings

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THAT IS NORMAL. The tank only completes the circuit for one element at a time. You should normally get 120v to earth from both legs of a 240v circuit, (180 degrees out of phase) only when the upper t-stat reaches temperature and switches power to the bottom. If you measure 240v across the upper element then the lower element will read just what you see. You will measure 0v from side to side of the lower element when upper t-stat is switched to complete the circuit for the upper element, because when the upper t-stat is on, the hot is supplied to just one side of the lower element, but the other side is disconnected. What you are measuring is an open circuit the same 120v on both sides of the element because there is no voltage drop across the element when the circuit is open. You could turn off the power, disconnect the wires from the lower element, then turn the power back on, only one wire will be hot. If you can turn the temperature on the upper t-stat down to below the existing water temp then the other wire to the bottom t-stat will read 120 to earth, and 240v between. Or if the upper t-stat reaches set point and it doesn't switch the lower element on then it could be that you did not get the right thermostat and it is not wired right.

They should be set the same,but the lower one can be set a few degrees cooler if you feel better about that.Only one element works at a time.The upper one works until the water temperature is reached in the upper half of the water heater then it switches to the bottom element to heat the lower half.This keeps hot water flowing longer when it is being drawn for showers.The lower element is always the one that works harder because the cold water is pushed to the bottom through a tube so it always comes on first and if small amounts of hot water are used the upper element may not even come on.

There should be one thermostat that controls both heating elements. It is the big one on the top. The other one is just a sensor. The elements take turns heating the water. The reason there are two, is for safety reasons. If one gets stuck, you do not get boiled. Never turn them up too high! If there are two different settings, keep them both below 105 if you have children or older people that have slower reaction time.

ya thats no problem one or the works at a time only

The answer titled "BEST ANSWER" IS TOTALLY wrong! tHE UPPER ELEMENT aLWAYS COMES ON FIRST. bE GUIDED ACCORDINGLY!

Normally yes, that way one of them won't work harder than the other. This will also prolong their life span.

no they are for seting temp the heater turns on and off