You likely have a broken or faulty valve. To check the difference you will need to take the valve out and see if it is simply dirt or debris caught in the valve preventing it from closing, or a crack in the valve caused by freezing. Check on YouTube for a video instruction on how to take apart and repair your specific brand and model. The whole repair shouldn’t take a novice, like myself(as I had this same problem last year) more than a couple hours to completely repair.