Why won't hot water come after timer of recirculating pump is off?
Probably a failed/stuck/jammed check valve, if this was the typical (maketh me shudder) retrofit installation where the hot water recirculation line is the cold water line. That makes the proper operation utterly dependent on the check valve, or the cold water line can happily backfeed into the hot water.

The less-shudder-inducing system I prefer is a dedicated recirculation return line, but that can be hard to retrofit (and can have the same problem, if a bit less, since it normally returns to the cold side of the hot water heater.)