I have a hot water recirc pump installed and it has been working fine ever since I bought the house (5 years ago). Recently though the shower in our master bedroom - the one furthest from the water heater - doesn't get hot water much at all unless the pump is on. Since we have it on a timer we only have it set to go on in the morning and it works fine. When I come home from work I like to shower but when I turn on the shower I don't get hot water. I have left it on for 20 minutes. A sink in another bedroom runs hot in 2 minutes. What could have happened? Thank you!

We would have to know the configuration of the return line. Does it loop to the master bath room? Most of the recirculating pumps are left on all the time. Are you asking the system to provide instant hot water with the pump off? If the system's working and the pumps running a two minute wait for hot water is unacceptable. What am I missing here?: Regards, Tom

The pump is on a timer and works great when it is ON. I don't like to keep it on all day since it is a waste of energy. So in the evening when I shower it usually takes 3-5 minutes to get hot water but lately I don't any hot water at all unless I turn the pump ON. Not sure of configuration of the return line. The recirc is a grundfos 15-18SU?

Then you are attempting to get instant hot water with the pump shut down.
Why not set your timer to have the pump come on before you shower? They don't use much power, that's why most people run them 24/7. Regards, Tom

I don't want instant and I shower at different times each night so I would rather not keep it on each night for a 3 hour window. I used to wait 3-5 minutes and that was fine but now I don't get hot water at all. May have nothing to do with the recirc but I can't figure it out. Thanks

If you get hot water with the pump on but not with it off then it's a nobrainer. If the people in my area had to wait 3 to 5 minutes for hot water with a recirculating system in place I would be loaded with complaints and service calls. That kind of a wait is why we installed them in the first place. Good luck, Tom

Here is an excerpt from: Hot Water Recirculation Systems

Hot water recirculation systems can be activated by the push of a button, or by a thermostat, timer or motion sensor. Systems that use a thermostat or timer automatically turn on the pump whenever water temperature drops below a set-point, or when the timer reaches a setting. These systems ensure that hot water is always available at the faucet without any waiting.

Some of the commercial systems place a pump at the furthest H/C fixure and have a timer and thermostat. Either/or can kick in the re-circulator. The timer can assure hot water for the morning shower. The temperature sensor just gives it a kick now and then.

The temperature sensor could have become unbonded.