1. Buy string coated with graphite at plumbing or hardware store made for this purpose.
2. Turn off heat at thermostat or furnace
3. Remove valve knob
4. Remove top nut (you may find more string underneath- if so remove and wipe off any grease)
5. Cut approx 2 in of new string+graphite and wrap around shaft in a clockwise fashion (the same direction that the nut will be retightened)
6. Put nut back on- tighten until resistance felt
7. Put knob back on then turn on heat
8. If still leaky, tighten nut little by little until sealed.
9. If you mess with the valve alot, be prepared to repeat this every couple of years.