pilot light out?

My pilot light goes out. If I bypass the safety switch it runs forever. Switch was replaced 6 months ago. After resetting switch, heater runs for 10 min to 1/2 hour. It happened last year and I adjusted the pilot light cause it was making a fluttering sound. It worked for about six months. Now pilot is going out again. When operating, pilot flame seems normal. It's a Williams 35,000 btu wall unit, late 90's era