It would be very unusual for the water for your yard sprinklers to be running through your tankless water heater. Look for some other cause of your flow loss. Is there a cartridge water filter, for example?Although I dont know the brand of my tankless system, since it was installed 2 years ago, in my backyard i can only drive one water sprayer; before the tankless I could drive front yard and backyard at the same time, up to 5 sprayers. Now, I can barely drive one sprinkler. what gives?