Water Heaters - no hot water in the morning

For the past several months I have been having issues with my 5 year old Jetglas gas water heater in the morning.The first shower of the day is usually(not always) luke warm at best.The second shower is always fine. If I put the wash on prior to the first shower,then the first shower will be hot.I can also accomplish this by running hot (warm)water from the fawcet until I hear the water heater's burner kick on.This usually takes about 3-5 minutes.What's going on here? Is there anything I can do short of calling a plumber? Thanks.

This is not uncommon with gas water heaters. It is not really a "fault" but simply the nature of the beast. Just running a few minutes of hot water ten or twenty minutes prior to your shower is the easiest and least expensive fix.

My 50 gal Rheem is now doing the same thing. This gas heater is approx 9 years old and just started doing this.

I am selling the house in a month, so I don't want to replace the entire water heater. However, if just replacing a part would help, I would not mind doing that.

Would replacing the thermostat or thermocouple (recommended by Lowes) help?

If your pilot light is not going out then replacing the thermocouple would do nothing.

Replacing the thermostatic gas valve might work but a nine-year-old gas water heater is running on borrowed time already. I would be hesitant to disturb any of the piping (including gas piping) on that old of a heater lest it would REALLY start having problems.

Do you have hard water in your area? Have you done routine maintenance such as draining or flushing of this heater on a regular basis? If not, then doing anything could cause the water heater to start leaking.