If your water heater seems to produce less hot water than it used to, look for these possible problems.
one problem may be due do extreme cold water temp going into heater especially in the winter these problems can not be remideed, the only thing you can do is turn the thermostat up slightly.

A broken dip tube inside the unit is sometimes another cause. this tube goes down into the tank about 42 inches. the only way to replace this is to disconnect the cold water feed and remove and replace the tube. since this sits so low into the tank you need to make sure you have enough clearence at the top of the tank to remove