I have a old furnace standing pilot and it did not stay lite.so I replaced the thermcouple and it work for
3 months.and know it happen again. But know I can't kep the pilot to stay on.just wondering if it was a bad gas valve.thanks

Take the pilot apart and make sure the orifice is clean. Many times the pilot light itself will be to small to keep the thermocouple activated. This is usually caused by a restricted orifice. Easy does it on the little orifice since it is a very small drill bit number size. Do not poke something through it trying to clean it unless the wire you use is smaller than the orifice size to start with.