The Lance J. Technoweb

There is a lot of garbage out there in terms of how hot domestic hot water should be.  The standard advice is 120 °F, and I agree with that. Some amateurs are trying to convince people to turn up the heat to dangerous levels, or even to replace their hot water heater due to "Legionnaires' disease".  But legionnaires is all about warm air being blown over an poorly maintained air conditioner's stagnant waste water, and has nothing to do with a very low oxygen environment within an enclosed heated vessel.  Some pundits also claim that minerals at the bottom of the tank will somehow cause legionnaires, unaware that the cold water pipe releases cold water at the bottom of the tank. The short of it is: 120°F is correct. If 120 °F isn't hot enough, then the shower valve hot limit setting is mis-adjusted, or the tank is grossly undersized and cannot properly provide for the home.  A call to the plumber to fix the issue is in order.