Water Heaters - Gas Water Heater/Water temperature

I have a 5 year old gas-operated tank water heater that has required to be set to higher temperature settings over the past five months or so. For the first four years of its life, the thermostat was set to the energy saving level, and the water temperature was just right. (I actually never measured the temperature). As the water temperature constantly fell over the months, I have had to gradually re-set the thermostat to higher levels. It is now set almost as high as it will go, and I am afraid it will soon be necessary to set it to its highest level.

Is this a problem with the thermostat or with the heater itself?

I have flushed the heater a few times; this made no difference, and I didn't see any minerals or other sediments in the water.

Check to see if you have a hot water leak somewhere ( water running when every tap is turned off) or if you have a recirc loop, it could be a cross connect

If no other problems are found, (such as those mentioned in previous post or a bad dip tube), you likely have a bad thermostat. I see this quite a bit. As you have found out, raising the temperature will offer a temporary fix. It may, at some point be too cool, even at the highest setting.

The only fix is a new thermostat/gas control. However, it may not be worth spending the money on an older heater.