You need a new gas control valve.
A gal I've done a little work for has a 7 yr old Richmond water heater. I've replaced the thermocouple but the pilot still goes out after a few hours. Any deas would be appreciated.
not a licensed plumber
There can be more than one cause of the pilot going out, and the only way to determine which is the cause would be to watch it in operation. In many cases, if you replace the control valve, you still have the problem. And, I would replace the heater before I would spend time and money on a new gas valve.
I agree with hj.
Also make sure the thermocouple is positioned in the flame properly. And that there is no draft causing the pilot flame to go out.
Have a great day.