Understanding tankless recirculating water heaters

Cinch rings will work as long as they are meant for 3/4" pex. I see millimeter on the package. Be 100% sure they are correct to use on 3/4" pex pipe. The black crimp type rings (they are really copper) is what you already have in the house. I prefer them over cinch. It gets to looking like a mess mixing connection methods. The cinch tool works for other size cinch rings so It could be useful for other plumbing projects.

I believe you have a pump in place in the heater so controlling with a button is the aim. You don't want it to run for any longer than is needed to prevent wear on the heater or pipes.

I've hacked in the unit below before. It is not as easy as plug and play but it's simple enough for those with the skills needed. How well the wireless works for your application is a thing to consider. It runs the pump for 5 mins. when the button is pressed. It is not adjustable for shorter times. If you know how long it takes for hot water to begin to arrive at the remote location and you turn on a hot water tap or shower before the tankless heater turns off due to reaching its set point in the recirculation line, there will be no cold water sandwich created. If you wait too long the recirc. line gets hot and the heater will turn off. Then when you draw hot water the heater has a short delay in turning on. Some cold water is let through the heater unheated and you get a brief temperature fluctuation heading to you in the hot water line. For most, once they understand what's happening, it is not a big deal. The clever hit the button and wait just the right amount of time to open the faucet and they get consistent hot water.

https://blackhawksupply.com/products/aquamotion-amk-wb

@Ghost_Rider357 It's very hard to advise you on how to proceed. Using the factory control is the best and easiest option. I'm not familiar with the logic control on that BW tankless what the setting are and I don't know if your pump is functional. A must is a complete recirc. line air purge, as I described previously. The line will not circulate at all, even with a working pump, with air in the line. If there's no air in the line and the pump works, the recirc. line should get hot once the circulation control time period is active. How long it stays on and what cycles and what temperatures measured where are is questions for tech support. It looks like that unit has a set up flow valve calibration procedure. It also has multiple recirculation control modes. The mode needs to be set correctly for your system. One mode uses an external NTC sensor and another an external aqua stat. External meaning a part mounted on the recirulation line. One of these parts will need to be installed to keep the line properly hot. No schedule will work until the unit has the proper time is set in it. I recommend reading the manual well, develop a good understanding of what you think is the right programing is and then confirm that with tech support.

@Ghost_Rider357 Just a heads up. The push button device I posted above is a stand alone electrical control. I don't know if you can use it with your heaters existing internal pump or with an added external pump. Your heater has flow control valves and a small tank involved inside it. It may be more complex than just turning the pump on and off, It also might be just that simple. Using the stand alone control requires someone with the tech skills to determine if it can or be done correctly. It's best to try to make the stock unit work as it was designed to. Your heater has more than a few different installer level mode settings for different types of recirulation control. Two of them involve an external sensor or a thermostatic switch. One of external parts sense the temperature at a place on the recirulation piping away from the heater. There may be other setting that change the control behavior or the water flow path or both for a given type of system. The senor or switch tells the unit when the recirc. line has heated up so it knows when to turn off. It likely then waits for a given off period until it cycles the pump on again reheating the line cycling like this during the timed heating period. How hot it makes the line and how long it turns off and when in that repeating cycle you happen to draw hot water will determine what you experience. The problem you were experiencing and correct recirc. mode settings are different things. You haven't said if you have purged the air. It's unclear to me if the recirc. line does sometimes heat or not. If your time is set correctly in the unit and you know when it turns on in the morning you can be there for that event. Listen for the heater to fire up on its own to heat up the line. You can confirm the line gets hot by feeling it a few ft away from the unit. It should only take a few minutes. If the unit fire up but the line never gets hot, something is wrong beyond programing.