We have an inground sprinkler system with an electric booster motor for greater pressure and volume. When it turns on (or perhaps when switching between zones?) it causes the toilet filler valve in our powder room (the only bathroom affected) to run, filling the tank to the point the water flows continuously into the overflow pipe.
The sprinkler consumes a lot of water. I don't understand how the diversion of water pressure away from the indoor plumbing would cause this.
What's the fix?