Have a very old AO Smith water heater model #FGR 40 224. Having trouble with the pilot light staying lit and replaced the thermocouple which didn't solve the problem. Pilot light will still not stay lit. If I wait for the water in the tank to cool eventually I can light the pilot and the burner will light and reheat the water. If I need to replace the thermostat might as well bet a new water heater.