The valve has to seat on both sides, and a poorly seating valve will burn and lose a piece of the seating.
As it is pretty small in the first place, the biggest thing you can do wrong is not to screw it tightly down, whichever way you are moving it, allowing dirt to get under the seat.
There are copper washers that seal the housing and inner chamber half, make sure these are in good shape.
Also make sure the pressure spring on the spindle is OK and not broken.
Peter