Will the Grundfos 599388 24-hour timer fit the Comfort System (595916).recirculator?

SOURCE: grundfos recirculating retro fit hot water out of the cold side

they have it installed wrong it is pulling from the wrong side, it is supposed to pull ot water up to the fixture but then if it stays hot on the cold side they are backwards

SOURCE: Problem with valves in Grundfos hot water recirculation system.

Yes, you need to replace it.

SOURCE: Grundfos recirculating system. Never has

http://waterheatertimer.org/Water-heater-recirculation-system.html

The circulation system should draw hot water directly from the water heater as shown on illustrations on link above.

The Grundfos pump works on a thermostat, and some work on a timer.
Can you hear the pump working?
There should be a humming sound.
Check the timer -or- thermostat setting.

It is possible the lines are clogged with sediment if you have hard water.

If I was going to fix the problem:
1) check thermostat or timer
2) listen for pump sound
3) check electricity going to unit
4) take apart the pipes and inspect for clogging
If there is a clog, I would flush the line or soak the part in CLR (calcium lime rust remover)

The circulation pumps are sealed and there is no way to take apart the motor, timer, or thermostat for repairs.

add a comment if you need more assistance.