Lived in my house 10+ years. There is a recirculating system built next to the water heater. With the pump not running, I had found that the hot water arrived at the shower head quicker with the valves next to the recirculating pump left open than closed. I didn't know why, so I never ran the pump and the shower water got warm in 15 seconds or less. Recently, a plumber replaced the old Rheem which started to corrode at the top with a new Rheem. Now, hot water in shower does not get warm until at least 2.5 minutes later. Even with recirculating running, the time is only slightly shorter. The plumber suggests replacing the pump with a larger one, but that is missing the point. I am totally puzzled. Wonder if anyone can diagnose the problem.
By the way, the recircuating pipe to the side of the pump next to the tank feels slightly warm and the other side remains cold even after I run the pump for some time. I have an identical setup in another part of the house and the pipes on both sides of the pump warm up not long after I run the pump. Does this tell you anything about the problem? :(