I remodeled my bathroom last year - before finishing the install of my shower fixtures I had to turn water in the house back on - so I capped the pipes off with the fittings in place, without handles I couldn't tell if they were 'off' or 'on' - and I turned the water on.
Water was then luke-warm in the back bathroom: I capped off my pipes while one of the faucets was on - which was feeding cold water into the warm water line.
I had to turn it off, disconnect it all, cap it, and didn't try to reconnect without the knobs in place so I could see where 'off and on' were. . . problem solved.
(just some new two bits)
I'm a giiirl - The local hardware store is my shopping mall ;)