Pilot will nost stay lit!

I went to turn on heater and noticed it did not make normal noise. I noticed pilot was out and went through steps to relight. Observing pilot light when holding "gas control lever" all the way to left, set pos.,pilot lit but after holding for 1 min. went out. Made 3 attempts but went out after each time. Looking at pilot flame, it looked like nozzle was melted. Could it just be dirty? or need replaceed? This unit has worked flawlessly for 5 or 6 years.Any help would be greatly appreciated!