If you have a constant flow of water to a sprinkler head, you should be
able to trace it by sound. Get a piece of pipe and use it like a
stethoscope to trace the water flow, which will certainly lead you to
the control valve.

wrote:
I've got an underground sprinkler that stays on all the time. It looks
like we have seven zones in the yard. We found a buried control box for
four zones, unfortunately not the one that controls the suspect
sprinkler. We've been all over the yard and can't find a second control
box. Any suggestions on how we can locate the second control box is
greatly appreciated. As you may surmise, we're not the original owner
of the home.
Thanks in advance.