sounds like a dirty pilot.althought pilot lights,the flame is soft and is taken-out by the burner going off.dirt may be either under the pilot orifice,or laying on the orifice.while the pilot is lit and the burner is on,gently tap on the pilot gas line.this will disturb the dirt enough to allow the gas pressure to blow the dirt off the surface of the orifice.if,however,this does not improve the pilot,the pilot assembly will have to be removed and cleaned.