I have a four zone system, all with 4 sprinkler heads. Zones 1,2 and 4 work great. The sprinklers in zone 3 do not pop up when the zone is on although water is flowing out. If you manually pull all the sprinklers up the sprinklers in this zone work great and seem to have good pressure. The sprinklers will not work correctly until all four are pulled up. Any ideas?