Thanks @DLane !
I am able to fix it. It turns out to be bad solenoid. I replaced it and now my zones are live and no zone fault notifications from Rachio! To get there, I did lot of troubleshooting. Adding those notes below for anyone researching zone faults in future.
I borrowed new power supply from neighbor’s Rachio. I still got zone faults with this power supply. So power supply is ruled out.
Then I went to Home Depot, bought two Hunter PGP inline valves and sprinkler wire. Connected one of them to Rachio master port. Other one to zone 11. Connected common port to both the valve’s common port. Then I ran zone 11. I heard clicks from both the valves and Rachio didn’t restart nor did it popup zone fault. That told me controller is not problem. It is outside in the yard.
I went back to Home Depot and bought three different types of solenoids (rainbird, hunter and orbit). Then came back and started locating valve boxes. This part took a while. I took a Philips screw driver and started poking in the ground. I found a valve box close to valve box that houses all the wiring before it goes to sprinkler controller. That turned out to be one of the zones. It is not master valve.
After 20 minutes of frantic poking in the front yard starting from city water line, I found another valve box located below front shrubs.
I turned the knob 90 degrees on the back flow preventor (I think) so that water doesn’t come to main valve. Then I completely unscrewed the solenoid. Then water started gushing out and started hitting up 3-4 ft high. The damn back flow preventor has two knobs. I didn’t realize I had to turn both of them off. Once done, flooding from master valve came under control.
Spent 10-15 minutes draining water from the valve box. Once the solenoid inlet is visible, I disconnected old one and connected new one.
Then Ran a zone. Controller didn’t report zone fault. That was great sign. Then opened the water line partially to sprinkler system. Then ran a zone. Bingo! The zone sprinkler heads popped up and started watering. Repeated this on couple of zones. Everything seemed to be working fine now.
I am rerunning the schedules that were skipped last week.
Had I called a irrigation pro, I probably would have paid $200-300. In the end, It is $8 solenoid and $5 waterproof wire nuts for parts and time I spent troubleshooting this.
Conclusion: Rachio saved the day. It is the best sprinkler controller! Period.