Low pressure on one sprinkler zone can come from water escaping through a leak or from flow being restricted before it reaches the heads. Comparing symptoms across the zone helps separate the possibilities.
Clues that suggest a leak
Wet soil, bubbling water, one unusually saturated area or a sudden drop in performance can point toward broken piping or fittings.
Clues that suggest a valve restriction
A valve that does not open fully can reduce flow across the entire zone without producing an obvious wet spot.
Why head problems still matter
Multiple damaged heads or incorrect nozzles can also change zone performance, so diagnosis should consider distribution as well as supply.