I think if there were debris in the lines downstream from the zone3
valve, at least some of the heads would get some water and work.

My guess would be that some debris got into the supply line (manifold)
upstream of the zone3 valve and is blocking flow to the valve and
everything downstream in that zone. Perhaps when the zone1 valve
cracked, a piece got into the line (or something got in while you were
replacing the zone1 valve) and lodged against the zone3 valve. Try
removing the zone3 valve and flushing the manifold; inspect the zone3
valve also to see if something lodged in there.

sweetft5 wrote:
I have a sprinkler system with three zones, I just replaced the valve
for Zone1 as it had cracked, and all three zones worked for about a
week and now when the controller reaches zone3 the heads don't pop up
and it sounds like the water backs up (the copper pipe leading from the
house into the ground shakes quite violently and can no longer hear
running water). I am wondering if this might be most likely caused by
a clog in the sprinkler lines or a problem with the Zone3 valve or
something else. I have opened up the heads on the Zone3 sprinklers and
they are dry. Thank you for any suggestions you might have.