Why am I getting cold water at faucets near the end of a circulation loop?
I know this is a year later, but I finally got around to getting this addressed. I decided to service my water heater - drain the tank, replace the anode rod, and replace the check valve. Sure enough, the inside of the valve was gummed up, with the little disc stuck in the open position. This most likely explains why our tub could get "warm" water instead of "hot" water after a few minutes.