Hey @Naughtok-
I am sorry to hear that Rachio isn’t able to easily work within your restrictions! @DLane mentioned that you can plug two zones wires into a single terminal. I hope this may be able to solve your issue. While I will tell you this is on our roadmap, I cannot give any anticipated dates. If @DLane’s solution does not help, please let me know and I would be happy to find something that is more fitting to your needs.
McKynzee 
This is a very long topic, but I’ll throw in that I have a 1 hour drip zone, a 30 minute drip zone, and neither has very high flow. Days that all my zones run, watch out! It takes many hours to finish all the schedules.
Since the best time to water is a fairly narrow window of time (not too early to avoid fungus & infection, not too late to avoid heat & wind) a long run time is not desirable.
It would be easy to cut my runtimes in half by running the drip zones in parallel with the sprinkler zones, and I see in this thread that electrically the Rachio can support running two valves at the same time.
This might not be anybody’s first choice, but thinking that getting a second dumb controller, or keeping the old controller you retired when you got your Rachio to operate some zones on a fixed schedule while you use the Rachio for weather-based scheduling for zones that benefit from flexible scheduling the most. Each controller could operate it’s zones independently.
Not ideal, but might provide some relief at a cost if you have hard scheduling constraints.
You say Rochio can run three solenoids at once. Is this an electrical power limitation? Is there any way I could run tie 3 or even 4 zones into a single terminal?
@Naughtok the biggest limitation will be the power rating of the power supply which came with your Rachio. It is enough to supply 1 Amp of current before the voltage starts dropping and power supply / cable heating up beyond the specifications.
The second limiting factor is the power rating of the internal switching thyristors (components which allow Rachio to turn ON/OFF your zones). The more current they have to supply, the faster they will heat-up and break.
Finally rachio is usually monitoring the current reading of individual zones and may shut down the overloaded zone thinking that there is a short circuit somewhere.
Overall you can run pretty much unlimited number of zones off of one terminal, but you would need to use a beefy relay (such as a pump relay or something similar) and the power supply capable of providing about 250 mA per solenoid you wish to run (so if you wish to run 10 solenoids, it will take a 2.5 Amp AC supply, which is about 60VA power rating for a transformer).
Cheers,
Gene
@Naughtok - as @Gene pointed out there are some electrical component limitations in the Rachio. Then, I think the wire gauge and distance out to the solenoids along with the individual actual solenoid power draw come into play. If the installation doesn’t have a master valve or pump start relay installed one could attempt three wires in one terminal. If so, I’d send a request to Rachio support after it has run to see what the current load is and how close that is to the limit for a single zone. If there is only one zone that needs three solenoids running at once, and the master valve and pump start relay aren’t used, I’d split the load between the zone and the MV terminals using a 24 VAC SPST NO relay to power two of the zones. In this set up the zone terminal would power one solenoid and the relay coil and the MV terminal would be connected through the throw on the relay to the two other solenoids.
The use case here is to turn on the (organic) inline mosquito-control for the last 2 minutes of each zone. I’d have a diversion set up after the master valve, that can divert the flow to go through a chemical injector before going out the various zones.
I also have several low pressure / drip zones that can be run at the same time, and it would be nice to be able to irrigate when it’s best for the plants, to prevent fungus issues.
How about having an “advanced mode” available that can unlock this feature? Just add a warning that you need to know what you’re doing in terms of water pressure/flow in order to use that mode. I’m exploring whether I should return my device.
Is should not be necessary to irrigate the entire property every day. Rachio gives the ability to set different schedules. You can also set water windows (predetermined limits on how long you can water on any given day).
I’m hoping to revive this ask for the ability to run multiple zones simultaneously.
First of all let me say that I love the Rachio product! This product is way better any previous automated sprinkler system controller I have used (including my last system by a company starting with Irri).
Now the bad news… at my last dinner party with 10 of my closest friends from college, I was impressing them with my ability to turn my landscape lights on with my phone. Then, they wanted to see my waterfall run. The only way I could turn on the waterfall is to turn off the lights, because I was not able to run both zones simultaneously. It was nighttime. My friends DID say they enjoyed the sound of my waterfall even though they could see the water. 
Lights and waterfall pump are controlled through relays.
BTW… the other (Irri…) company’s product handles this fine (they have a lighting zone… hey!?)
Thanks for reading.
Why not just buy a Wink hub or similar to control these?
Will the new Gen 3 finally run multiple zones simultaneously? I had to buy 2 controllers and jump through hoops to program schedules in order to accomplish this. Not the easy use case for which I was hoping, or as cost effective.
Why buy and hook up additional components when I already have what I need once the software feature set catches up.
Well, my irrigation system can run multiple zones at once without issue, so I personally have no issue if the system ran more than one zone at a time, but many on wells or pumps cannot run more than one, so it is imperative that the system does not allow it.
Rachio is an irrigation controller and doesn’t tout itself as anything other than that. To me it just seems a bit silly to complain that it doesn’t have a feature to control something it wasn’t designed to control.
You are certainly entitled to your opinion, but I don’t quite understand why you are voicing it against my request. I do appreciate that you have provided me with a potential alternate approach (thanks)… but with additional cost.
Rachio:
What I have suggested is a potential additinal revenue stream for your same hardware. Your competition provides an option to run lights with the same controller which runs sprinklers. If you identify these lines which can be run simultaneously as for lighting functionality (as your competition does) it would be clear to your irrigation users.
@azbob, no the Rachio 3 will not support this due to electrical limitations. Out of curiosity, why do you want to run two zones at once?
@calif_ken thanks for the suggestion. Lighting is an interesting use for the controller. We don’t have any plans to support this in the near future.
I want to run multiple zones simultaneously because I have 15 zones, drip irrigation in AZ, for trees and plants. Because each zone runs between 1-4 hours, there are times when two zones may have to run concurrently. Additionally, I check the zones weekly by turning one on at a time. If I do this when two zones are already running automatically, there would be 3 zones running concurrently. My old Irritrol controller handled this with no problem. I had to buy 2 of your controllers to get around your limitation and jump through hoops to set the schedules. It is a pain and it makes my life more difficult. I have been asking you to fix this for 2 years with no result.
I understand your desire and need for this; however, this is a residential controller. Step up to high end commercial smart controllers and you can do this. But the cost is at least $2,000. Examples include WeatherTrak or Rainmaster Eagle Plus.
My previous residential controller did this. My understanding is that a number of residential controllers do it. It is not uncommon.
@azbob, thanks for the additional comments. Do the two controllers you currently setup handle all of your zones? Assuming you have enough pressure to water multiple zones at once, a work around might be to double up your zones (assuming you don’t have a master valve or use the WaterHammer feature). This would allow you to schedule your entire system on one controller and sell the extra controller. Alternatively, you could run both controllers at once to help shorten your overall watering duration.
If neither of these solutions work for you, let’s help you find a controller that will better meet your needs. In full transparency, we don’t plan to support this feature in the near future as commercial grade hardware will need to be developed.