According to Ray K :
There is a misunderstanding about my configuration. There are five, not
three, heads in the problem zone. The two lowest ones dribble; nothing
at all out of the other three. If the dribbling ones were plugged up
with grit, that would restrict flow through those heads and increase
pressure to the remaining ones, which should then have a greater
tendency to rise and squirt water farther than when all five are
working. Am I missing something?

I knew there were five, but I thought the other 3 were working normally.

So, to be sure I understand, the string has 5 heads. The first
three (going outwards from the valve) aren't emitting any water,
and the last two are dribbling.

That's suggestive that the valve is defective. I _know_ you're
saying that the water meter seems to indicate that water is
flowing in this circuit, but I find it hard to believe that
a leak would result in the three heads _first_ in the string
get no water, and the last two dribble. The leak
rate would have to be horrendous (as in virtual severing).

There should still be enough backpressure to get _something_
out of the first three.

Unless something like: the first three are MUCH higher than
the valve, and the last two are much lower than the first
three.

If you lay bricks on the dribbling two, do the other three
start to dribble?

I think you're going to have to start considering disconnecting
the line at the valve and check for full flow. Then, secondly,
start excavating around the heads.

[Apropos: after many years of trouble free spring restarting,
I have two zones (off a 6-way controller) that won't trigger
at all, and on the second controller (only runs two zone),
frost had stripped out the solenoid. I'm going to have
to start electrical diagnostics tonite...]

--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.