hot water

I am new to DIY plumbing projects. I am replacing the hot water cartridge in my shower but can not get it installed correctly as no matter what I seem to do the hot water will not turn off at the faucet once I turn the hot water on in the basement. I am open to any and all suggestions...

I live in Chandler, Az with very hot summers. My house is 6.5 years old and in the past 6 months I've had two very slow leaks cause ceiling damage. In both cases, it seems like there is hard water sediment on a hot water Pex line near a manifold. I had a few plumbers comment on the color of...