I have a system with three zones and recently, two heads in seperate zones do not fully pop-up when turned on. If I manually pull them up, water will come out, but at a reduced flow compared to the other heads. I tried replacing the heads, but it did not solve the problem. I am thinking possible obstruction or break. Last year the system worked fine, and this year, the only thing that I can think of is that on one head (Zone 1) there is a break somewhere even though I see no evidence of flooding...
