12 zones total. Troubleshoot low pressure on zone 12; Found 1 rotary head jammed from sand/sediment, was able to pull it up and clean it, however I recommended to replace it. Tested zones 10&11 and determined that the pressure is the same or not much better. Also found another head jammed, and was able to pull it up and clean it a little. Assessed zone valves in valve box: no problem found there. Assessed the well tank and plumbing: all valves are fully open. Pressure gauge at well tank reads approx 33 psi and stays steady…was not climbing. Advised customer that it is possible that the well pump is not performing 100%. It is also possible that the well tank is not functioning properly. Suggest having a well company service and set the flow rate performance. Current system is designed to require at least 15 gpm flow, since there are at least 6 heads per zone.