Hot Water Question - Help Please

There is a check valve on the outlet side (hot water) of the water heater. Since you can bypass the heater and run cold water and since hot water will come out the relief valve, the only thing left is the check valve which must be closed and not able to open under pressure. I doubt it is frozen shut since the water is hot. It will need to be replaced. The check valve is there to keep cold water from entering the hot water heater outlet since most do not have a valve on the outlet like some have shown in earlier posts. Most installations have an inlet valve and a bypass valve but no valve that is manually operated on the outlet (so they must have this check valve). Hope this helps.