When moved into a new house and there is a quirk with the lawn sprinklers. Now and then, one of the zones tries to fire, even when the system is set to off. It will squirt water for a second, stop, usually try again, stop and then it won't do it again until another 20 mins or so. Sometimes, inside the house this creates a audible clanking sound as the pipes sort of jolt. I notice that if I shut the outside sprinkler water supply off, this activity ceases. But if the water supply is on this quick will happen, even if the zone is shut off on the control box. Any ideas to look for?thanks!
The control valve for the zone may be worn or defective.
The typical control valve for a lawn sprinkler system is not a faucet that uses a washer pressed solidly against a seat or a turning ball with a channel through it to admit or cut off the water.
Instead there is a rubber disk with a small hole in the middle that is either covered or uncovered when an electric solenoid plunger similar to a door bell striker is activated. The disk then acts as a flap to let water by or close it off. I don't know exactly how it works but the term "vacuum break" seems to be used to describe it. A leak or a defect in the valve may unbalance the pressure or suction causing the disk to let water by and activate the sprinklers with the electricity off and a moment later the running water causes the pressure or suction to regain the level corresponding to water off.
Tornado victims: Do not rush to rebuild. Take your time and look for and get a good contractor. Or consider selling the property and moving to a home that is ready to live in.