They might be plugged up or defective. Some times when the connector is used to punch the hole in the 1/2" pipe it doesn't make a clean hole you might want to check that.

Here is a link that might be useful: do_it_your_self_site

Hi Aulani,

One more thing in addition to the above post is to make sure the number of sprinkler heads do not exceed the output of your water source. Each head uses a portion of the flow and pressure up to their rated amount. the ones closest to the source get their allotted amount, but the end of the line may only be getting a portion of the flow and pressure and don't operate efficiently or at all. If all heads are not working it is a source problem, if only ones close to the source get more water; then you need to limit the number of heads in that area and add more zones. Aloha.