LondonRain brought up some interesting insights that I'd like to explore further before committing my new design to a 2-wire system. I'm assuming that this is because the wire path between the decoders in the field and the valves themselves is not "open" unless the decoder is communicating with them? Can you trace between the controller and the decoders like in a multi-wire system? Do the decoders act kinda like an "isolation valve" in that signals only go between the decoder and the valves when the controller activates the decoder? That's a given on anything I install, anything major we repair or problematic systems where I will document main line and valve locations for future reference. Just yesterday I was able to reference a scaled "valve location as-built" I'd made up on a newer system (30+ field valves) where we didn't have an original contractor as-built. We had spent many hours locating the valves and putting them down on a plan since I just knew the site guy would not keep the boxes uncovered and I just knew that we'd have future problems since the original system was installed by one of our least favorite contractors. I was able to direct Leo via Nextel walkie-talkie to the general area where the suspect hung valve was located and he was able to locate it and reair the problems. He said I was within about 3' of where I'd indicated. What type of system decoders/controller does this one have? Are they installed in their own boxes or as part of the valve/box installation? Are they single, multiple valve decoders or a combination? By its very nature the decoders give you another level of "controller" interface and potential problems which could become a real PITA. Was this system installed by another contractor or did you do the install yourself?