Don’t forget that virtually everyone has a zone 1. Far more than those who have a zone 16.
statistics and all that jazz (yes, installers are likely to install zones starting with zone 1 even though that is not a requirement.
Rachio opens the door to the water pipe and holds it open for water to go through. Once it turns off power the door is supposed to close itself using a spring. Rachio is not involved in the closing. All rachio is doing is putting out enough electricity to hold that door open with more force than the spring that is trying to close it. I’m using the word door when the real word is valve, but i hope the visual will make it easier to internalize.
If you remove power from the rachio, perhaps by remove the wire to that zone or by removing power from the entire Rachio unit, and the valve still stays open then its not an electrical problem anymore -science suggests this is more likely to be a mechanical problem. Rachio does not have any batteries onboard to keep it powered in an outage (which honestly i think is a shame, i would have loved to have some amount of battery reserve living in the brown-out state of california, perhaps as an option). But for your purposes, once power is pulled the rachio is dead and valves are supposed to go to their dormant closed state.
I suggest that when you put in your new rachio there may be a fair amount of stop/start cycles done as a part of testing the installation, schedules and whatnot. This may contribute to a valves demise ie if you had a bad valve or a valve about to go bad, a bunch a stop/starts may contribute and make it happen about the time when you put in the rachio. The correlation with Rachio has less to do with the Rachio and more to do with with cycling a declining valves more than normal, thus there is a weak correlation with new sprinkler controller. The fact that it is a rachio is noise, any sprinkler controller could have made that happen if you cycled valves a lot as a part of installation.
In my case, i knew that my old controller had equally or even older valves than the old timer. I try to proactively replace valves before they go bad, so for me i replaced them all as a part of the rachio install. I knew i wanted filters for my valves, and i knew i wanted valves where the filter could be cleaned without taking apart the valve itself. I got a hunter valve, model Hunter - ACZ075-25. It has a 150 micron aluminum mesh screen that is easily cleaned from the outside as well as a pressure regulator.
It replaced 20 year old rainbird valves, that seemed to work but i’d rather be safe than sorry.
So far these valves have been great, and given the cost i think its a well made investment to pick good valves. Especially since a stuck zone here in the SF bay area can cost me hundreds of dollars in waterbills.
If you like to read about causation and correlation, this is a decent paper published in the UK.
Illusions of causality: how they bias our everyday thinking and how they could be reduced https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4488611/