SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Hi, I am new to this forum and also new to sprinkler system troubleshooting. I have been facing some peculiar issues with 3 (of valves that I just can not explain. So far, my contractor also has not been able to diagnose the issues and not returning my calls any more. These valves are controlling my front yard and are only about a year old. These were completely functional until some concrete work was done around them with the valves placed in a box below concrete level. Several issues came up after the work was completed. These are:
1) These 3 valves now can not be turned on from my control panel. I suspect a contact problem here with the ground wire even though the connections look fine. But, I am not sure whether that is the reason.
2) I can turn on the valves manually with flow control turned on properly. But, there is a peculiarity in this condition too. As what I had observed with other valves, the solenoid has to be rotated counter clockwise to open the valve. Interestingly, on these 3 valves, with the solenoid completely rotated in the clockwise direction (that the slider says off), the valves start flowing the water. The valves stop the water flow only when the slider is moved to the "on" position (counter-clockwise rotation).
3) Once the valves are turned on manually, irrespective of the position of the slider and the flow-control valve, I find water leaking out of the lowest sprinkler head. Just for this reason, I always have to shut off the main irrigation valve after watering my lawn and plants.

Any advice on how I should troubleshoot and rectify the problems will be appreciated.

SprinklerGuy: Thanks a lot for your reply. About valves to be installed 12" above the highest head - I became aware of this requirement only about a week back when I started doing some research on my issues. Obviously I expected my contractor to be a knowledgeable person, but he turned out to be just the opposite.On the issues:
Issue #2: "Regardeless of what the "slider" says...(more like a lever yes?)...leftie loosie rightie tightie.....loosie turns it on, tightie turns it off...it is working as intended...I'm not sure why the slider is backwards." -- The slider is more like a lever. Unfortunately, in my case -- "leftie loosie" turns the sprinklers off and "rightie tightie" turns then on. That's why I said that the behavior was peculiar.
Issue #3: Here's the situation --
a) Main Irrigation valve off, flow-control on Irritrol 2700 valves off - everything is fine.
b) Main Irrigation valve on, flow-control on Irritrol 2700 valves off - everything is fine.
c) Main Irrigation valve on, flow-control on Irritrol 2700 valves on, slider and solenoid in "leftie loosie" condition - everything is fine.
d) Main Irrigation valve on, flow-control on Irritrol 2700 valves on, slider and solenoid in "rightie tightie" condition - sprinklers come up and water the lawn.
e) Main Irrigation valve on, flow-control on Irritrol 2700 valves on, slider and solenoid in "leftie loosie" condition - sprinklers go down, but water leaks through the lowest head.
f) Main Irrigation valve on, flow-control on Irritrol 2700 valves off, slider and solenoid in "leftie loosie" or "rightie tightie" condition - water leaks through the lowest head.
g) Main Irrigation valve off, flow-control on Irritrol 2700 valves off, slider and solenoid in "leftie loosie" or "rightie tightie" condition - no more leaks.

Debris in the valve body is probably the case. If it is, how do I clean that up?

Thanks once again ....