Geno, Thanks for the reply. Ironically I found the website this afternoon that you sent me links to later. Thanks for your kindness. If I get someone else the problem is continuity test on both elements of Rheems 40 gallon water heater tested fine. Power to upper element but no power to lower element. Trying to determine to replace one or both thermostats. Below is volt test I did on top thermostat connections. T4 and L4 bring power to lower thermostat from top one. No power reads when tested lower element. I did a volt test based on the diagram on this website. L3 to T2 is to have power - NO POWER (Problem) L1 to L4 is to have power- Did have power L3 to L4 is not to have power- Ok with no power L3 to T4 is not to have power- OK with no power L3 to T2 is to have power- NO POWER (Problem) L3 to T4 is to have power- Did have power So does this still indicate both Thermostats to be replaced? Are you a plumber by the way? Thanks so much! Tom

OK Tom-- That is good thinking-- comparing your OHMs on the installed heaters, with OHM on a new one!-- Great thinking!
So-- since we are pretty confident that the installed elements are OK-- let's trace the voltages coming in.

Did you let the heater try to heat the tank?
For as I said before-- It is normal for just the TOP element to get voltage during start-up. This speeds the delivery of SOME hot water at the top of the tank (where all the hot water is drawn off from).
So-- are you getting hot water ? Do you hear the element sort of bubbling and crackling as the water heats AT THE TOP ONLY?

As the top thermostat gets satisfied,-- IT THEN TURNS ON THE POWER TO THE LOWER ELEMENT-- and then it concentrates on heating the WHOLE TANK.-- Make sense?

One more thing to think about:
If a heating element is OLD, and if you have a lot of Calcium building up around it (at the Bottom of the tank)-- The element can get overheated (due to a lack of good water circulation-- from too much calcium in the way..)
When it overheats, the element breaks thru it's metal jacket, and it can give a low resistance 'short' to ground. This can fool our Ohm meter into giving us a reading that LOOKS good,,, The best check for that, is an Ammeter (A clamp around kind) -- then we know we have current going thru the element, and HEATING WATER.
If you can get a hold of a clamp-around Amp meter, that might help you confirm that both elements are drawing the right number of amps.
Let me know what you need next-- I will be away most of the day-- I'll be back tonight to check on you..

Mack B OK Tom-- That is good thinking-- comparing your OHMs on the installed heaters, with OHM on a new one!-- Great thinking! So-- since we are pretty confident that the installed elements are OK-- let's trace the voltages coming in. Did you let the heater try to heat the tank? For as I said before-- It is normal for just the TOP element to get voltage during start-up. This speeds the delivery of SOME hot water at the top of the tank (where all the hot water is drawn off from). So-- are you getting hot water ? Do you hear the element sort of bubbling and crackling as the water heats AT THE TOP ONLY? As the top thermostat gets satisfied,-- IT THEN TURNS ON THE POWER TO THE LOWER ELEMENT-- and then it concentrates on heating the WHOLE TANK.-- Make sense? One more thing to think about: If a heating element is OLD, and if you have a lot of Calcium building up around it (at the Bottom of the tank)-- The element can get overheated (due to a lack of good water circulation-- from too much calcium in the way..) When it overheats, the element breaks thru it's metal jacket, and it can give a low resistance 'short' to ground. This can fool our Ohm meter into giving us a reading that LOOKS good,,, The best check for that, is an Ammeter (A clamp around kind) -- then we know we have current going thru the element, and HEATING WATER. If you can get a hold of a clamp-around Amp meter, that might help you confirm that both elements are drawing the right number of amps. Let me know what you need next-- I will be away most of the day-- I'll be back tonight to check on you.. Mack B