The irrigation head at the end of the line in one zone does not pop up and stay up to spray. It only trickles water when the head is removed from the line. The next head up in the line seems to work fine. This has been a problem since original installation by a professional. Upon calling the installer and he coming out to check the problem, he said that there was nothing wrong. But, it does not spray and does not stay up. Do you think we have a plugged or kinked line? Could there be a problem with the water pressure and is there a way to adjust that?