I have a 50 U.S. gallon water heater – model number MI50455LNH10, which is about six years old.
When my family goes away for a few days and the hot water does not get used, we return to luke warm water and are unable to even have a bath. It seems that when the tank has been inactive the temperature cools, and when we start to use the water again, the water temperature seems to go back up after a few hours.
When we go away I do not set the red temperature dial to “vacation”.
To further complicate the matter, the red temperature dial is almost set to max. Inspite of this unusually high setting we get hot water which is at a reasonable temperature. I would expect it to be too hot, but it is not.
The only external factor is that when we go away, I usually turn off the main water valve into the house. I do not know if this would make a difference or not.
The biggest difference would be whether you have a house when you returned. If the water is shut off then you must turn the valve to PILOT, otherwise a malfunctioning thermostat could overheat the water heater and if there is no freshwater supply the temperature/pressure relief valve will not be able to function to reduce the temperature and/or pressure and the heater could explode with the force of several sticks of dynamite.