Common underground sprinkler problems are broken sprinkler heads, low water pressure and entire zones not functioning. Broken sprinkler heads are easily identifiable, as the head is often cracked or broken and fails to pop out when water pressure is turned on.
Replace sprinkler heads by digging a hole around them, approximately one foot deep. Be careful not to damage the main line that feeds the sprinkler. Remove the broken head by rotating it counter clockwise.
Install the new head, set the sprinkler range and pattern, and test the sprinkler by turning it on. Be sure to check for leaks. Fill the hole with dirt. Low water pressure is commonly the result of a cracked or severed pipe.
Check the lawn for areas where water bubbles and areas that are very wet. Carefully dig until the pipe is found and repair the damaged portion. If entire zones are not functioning, a fuse may be blown and requires replacement.