The upper and lower elements take turns heating the water, you will never have power to both at the same time. The upper one heats the water in the upper part of the tank first. Once it reaches the set temperature, it will shut off and then send power to the lower element. So, give the upper one time to heat up before checking the lower one. To check the lower one, I set the upper to the lowest setting (so it would shut off quickly) and then had power to the lower one. Once I knew it was working I re-set the upper one to the desired temperature.