I have a sprinkler line that is using well water with a pump. All the heads
are working except for two shrub sprays. The only difference between that
and the rest is that these heads are mounted 3' off the ground on top of a
riser and the rest are flushed with the ground.

I have removed these two heads and connected to a garden hose, tested them
and they are working and open.

When I connect it back to the sprinkler line, nothing come out of them. I
flushed the line as well.

Is it possible for the heads to not work just because the heads are 3' off
the ground and not enough pressure?

Thanks,

MC