On Mon, 30 May 2016 12:55:27 -0400, "Kurt V. Ullman"
wrote:

I have a line of about 5 heads. The ones farthest away from the valve
are working perfectly. The 3 closest to valve only go part way up and if
I manually pull them up, they often stay up even after the water is
turned off.
The farther ones working would tend to argue against pressure
issues. Does it seem the best idea to just replace those three or is
there some other diagnostic trick I should try first?

Save the old ones in case I'm wrong. Maybe they can be cleaned,
although I guess if so, you should do that before buying new ones. Not
that I've ever cleaned one, but dirt is the biggest problem for almost
anything mechanical.