Gas Fire place. Pilot light comes on stays on. After starting the fire, both the pilot and the system fire went out in about 3 minutes. After several light cycles it now goes out in less than a minute. After it cools it still goes out but still less than 3 minutes. When this happens I can hear something close inside the Gas Valve Assely.mb Checked the readings between TP and TPTH with the pilot lit and it rises to 550 mv and gradually falls to 485mv and stabilizes. When the system is turned on the mv readings slowly drop from 485 downward but never gets to the 220mv before the system turns off. All the system holes and pilot light has been blown out and cleaned as well as the thernocouple. Any ideas as to what the problem might be or additional test that can be run. Thank you in advance.