Our gas water heater recently will only last one shower. The thermostat seems to work. The flame cycles when it should. There is no leak in the plumbing system within the house. The outlet pipe is warm to the touch prior to using the hot water. It quickly becomes luke warm to cold after filling a tub with 10 gallons (it’s a 50 gallon heater). The flame comes on as well shortly after running the water.
I was told by the manufacturer that the dip tube in this 3.5 year old water heater (with a 10 year warranty on tank/parts) has not had any problems reported (unlike the class action dip tube suit which affected its 6 year warranty model).