I asked the solar installer why he installed the check valve on the supply instead of the return and I was told it's a new law/requirement that the check valve be installed this way; they used to install the check valve on the return but not anymore. This doesn't make sense to me.
Also, if a check valve is installed on the return, it will not prevent the water in the vertical pipe to the roof from emptying, correct? I'm not really sure the reason for the check valve on the return.
Should I add a check valve to the return? Should it be a spring or flapper check valve?