Vacation mode is a setting on your water heater that allows you to run at lower temperature than normal, saving energy and money. Typically, manufacturers set vacation mode to around 50°F, well below the temperature you need to for a shower, but warm enough to prevent freezing while you’re away.  If you are going away for more than a few days, use the vacation mode setting, or if you have a digital readout, turn it down to 50°F. DON’T shut off the water heater entirely, to avoid potential freeze-ups or difficulties in restarting the heater. And when you return from vacation, don’t forget to turn the temperature back up at least one hour before you plan to shower. The temperature should normally be set to between 120° and 125°F, which usually corresponds to the “A” setting if your water heater control is marked as A, B, C, and VAC.