Originally Posted by chuck53
Looks like a check valve to me. Might be stuck closed or partially closed.
You may be right. If so, then it seems to me to be installed in the wrong place. When I went to the ShurFlo site, they showed an installation with a check valve but it was located at the pump outflow. According to other articles, the check valve is typically in place to prevent hot water from backing up into the system. I'll remove and try and clean it in case it's clogged. Seems like it's not really doing anything worthwhile where it is right now.