The upper thermostat only comes on in high demand situations. During normal operation, the bottom one comes on first. Once the bottom thermostat is satisfied it shuts off. In theory, if there is never high demand the upper will never come on.
Lets say water is hot and high demand starts. At the beginning, the upper thermostat (UT) and lower thermostat (LT) are satisfied.
- Water draws from tank top and is replaced by cold to the tank bottom. - LT hits low limit first and lower element kicks on. - At this point UT is still satisfied and it's element stays off. - High demand causes UT to hit low limit, - Simultaneously the lower element kicks off and the upper on. - When the UT is finally satisfied it shuts it's element off. - The lower element kicks back on until the LT is satisfied.
Both elements are never on at the same time. That's how the old fangled ones worked anyway.
In his case where something is wrong and the water is cold in the tank because it's been off, the tank should try to operate as high demand and be applying power to the upper element right off.