Believe it or not, sprinkler heads will not last forever. When sprinkler heads get older, they have a tendency to stick up even after the sprinklers have stopped running. This is because the shafts get worn or get sand in the grooves and don't operate up and down smoothly anymore. Rotor heads also stop turning when the grooves get worn out. Replacing old heads can be quickly done by unthreading the inside part of the sprinkler, leaving the case still attached, and screwing in the new one. To accomplish this, you will have to buy the exact same sprinkler brand.