Rotating heads not rotating
I recently moved into a house with an underground sprinkler system and am having a problem with the sprinklers not behaving correctly. The system is on an automatic timer and has a total of 5 zones with 4 zones each consisting of 4 Rainbird pop-up heads and 1 zone having mister nozzles. The home was built in 2004.
The problem is that some of the pop-up heads do not rotate when the timer switches to their zone, unless I manually close the main water valve from the irrigation pipe and then re-open it. All heads do pop up, but don't rotate around and instead stop at some point in the coverage arc. When I manually close the main water source and re-open it, all sprinklers in the active zone then work as they should for the duration of that zone. Otherwise it seems to be sort of random as to when they stop rotating. When the timer switches to the next zone, it may rotate for a few moments but then seems to consistently stop rotating.
I'm new to underground sprinkler systems (my other homes did not need them), so any advice or suggestions would be greatly appreciated.
Thanks,
Mark