Water heater stopped making enough hot water

[GregP2112]

Have a gas heater, the burner works, it makes hot water, but it runs out now a lot earlier than it did. I drained the tank/flushed, but still has an issue. I even turned up the heat setting on the thermosat.

Have a 40 gal tank, for example load of laundry done, 20 min later hot shower only had 2-3 min of hot water. thoughts?

 

[Mike M]

The sacrificial tube which is part of the outlet pipe is reduced in length due to corrosion. Just replace the tube and you will be back to like new. The tube is designed to corrode before the tank corrodes.