Our shower mixer was getting stuck when turning it. We took off the covers to see if there was any deposits etc that could be easily fixed. However, there weren't so we tried loosening/tightening the stem screws (don't know much/anything about plumbing) and now it is only running with a drip at best. Have tried lossening and tightening again, but to no avail. Any suggestions of how to fix this (at least to get it running with some water again until a plumber can come)?