Do the other solenoid valves work? If so, I assume it has to do with this particular valve (Weathermatic N100). I did find its electric spec online — the inrush and holding currents are on par with standard 24VAC valves (though it’s slightly higher). Do you happen to have a 9VDC or 12VDC power adapter? If so, give that a try (the DC adapter that comes with OpenSPrinkler DC is 7.5VDC), and those can increase the holding current which will hopefully make it work.