Ok well that's good, you should be good to go. I wouldn't worry about running water if it gets cold out. It'll just wind up costing you extra. As long as you keep your house at a reasonable temperature when your away. Now that's odd that there was no water pressure at first and the taps. First things first you need to have the water off to the house or isolate the shower. Post some pics of the valve. Personally never replaced an American standard shower valve, but usually there's a set screw to remove the handle, then remove the cover plate (typically two screws) and then post a pic, or if your able to figure it out then that great. American standard I believe has a lifetime warranty so if you want a free one you can probably call them and they should send you one. Worst case scenario, pull the cartridge out and go to Home Depot and get the replacement (if they carry them I'm not totally sure) sometimes if I have two people ill have the cartridge out, turn the water on for a few seconds and make sure you have water pressure at the valve, and it can flush any debris out. When your turn the water off be sure to open taps upstairs and down to drain the lines. Ideally if you can get the right cartridge before you replace then there's less down time. Let us know how it goes and feel free to ask any more questions and we will help the best we can!