About a year ago, we had a Grundfos recirculating pump installed. We use a timer on it for morning showers. Recently, after the timer goes off, and someone needs to use the master bath shower later, no hot water comes even after waiting quite a while. There is hot water in the other bathrooms and kitchen sink. Any suggestions about why this is happening? Thank you.
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.)