I have a 9 year old 50 gal propane hot water heater made by OC Smith. It has a hot water circulating pump attached that is on a timer. When the hot water pump is not on, it takes approx 4 minutes for hot water to get to the furthest point in the house. The heater is set so the water is approx 120 to125 degrees.
About 2 weeks ago something happened so that it now takes approx 15 minutes for semi-hot water to get to the furthest point. Without the hot water pump on, the water is only getting up to approx 100 degrees. However, when the pump comes on, the water will heat up to 125 degrees in about 1 minute.
My question is does anyone know why the water won't heat up to the 125 degree range without the pump on, but yet when the pump comes on, it gets to 125 very quickly.
The tank has been flushed on a regular basis and the check valve is working properly.

Regardless of whether you think that your check valve is working properly, the description of the problem paints a different picture. You have a bad check valve.

quote; the check valve is working properly.

There is almost NO WAY that you can be sure of that. You are describing what happens when a check valve fails.