Pilot Light Only Lights when Tank Is Cold.

[wrif101]

I have a Whirlpool 50 Gallon, 40k BTU natural Gas Hot water Header.
The Unit is about a 1 year old. I replaced the Thermocouple, and the symptoms are the same.
The venting to the system is not block and has been the same for the past 14 years.
If there is hot to warm water in the tank, the Pilot light will not stay lit.
The pilot lit does light, and will stay lit as long as I keep the pilot light (red) button depressed.
As soon as I let go it will go out.
When the water in the tank is cold or cool I can get the pilot light to stay lit. Then I switch it to the “ON” position, and the burn fires up and the system seem to work properly. It will continue to burn until the water in the tank is hot.
Looks like when the system identifies that the water has reached temperature, or the system thinks it is overheating. It shuts the burner down and the pilot will go out. Then the cycle repeats as soo as the tank is cold/cool it will light.

I’m thinking that it may be the thermostat control and/or value in the control that’s bad?

Thanks Craig