I installed a new 50 gallon water heater yesterday and I now have a recurring problem with the unit. I can light the pilot and fire up the burner for about 5 minutes. After 5 minutes, both the burner AND the pilot light go out. It is easy to relight however, the same thing happens again and again. The unit is an A O Smith (propane) 50 gallon with Piezo ignition. I can see the thermocupler glowing. Have you any ideas as to the nature of my problem? Thank you.