Help...no H2O coming out of pop up sprinkler heads

Hi Terry-I have a Hunter Pro C sprinkler system...this morning I noticed that in zone 7- 2 of the 5 sprinkler heads were popping up as they should but no water was coming out of them. The soil around the heads is moist but there is no apparent leak I can see surrounding the heads. There is no water even dribbling out of the heads...please give me your suggestions-thanks, Mitzi

If a head pops up, it has water pressure. The nozzle, or the strainer below the nozzle, is clogged up.