My son is having a problem getting enough hot water. He has an older gas water heater that had been working fine until a couple of weeks ago, could not get enough hot water without turning the temperature control all the way up. I'm thinking it may be the thermocouple ? I had a similar problem a few years ago but it turned out to be a leak in the hot water line under the slab. I have also had the thermocouple problem as well.