I have a pressure switch question-

I just installed a well,tank etc.. for my sprinkler system. The problem I am having is as follows- The system comes on when the timer asks for it to do so, but it seems that at least once a day, the pressure switch does not cut in and allows the pressure to go to 0.. If I set the switch to start then auto , it will start again and runs fine. Any thoughts?

Thanks for your time - Len