Navien tankless water heater issue - recirculating pump?

[Jason464]

Navien npe 180a/210a/240a gas tankless water heater has slowly taken longer and longer to heat. I opened the unit and see this in the internal circulation pump and condensation on the bottom of the heat exchanger. When I drain the entire system and turn it back on, it operates perfectly and delivers the right temperature water quickly. But as use continues, I hit may 106 degrees in temp and it takes a while to get there. Am I able to clean the circulation pump or should it be replaced? Guessing this is hard water buildup over time? Any other thoughts?

 

[breplum]

That red tipped air vent has been fouled with hard water and should be replaced.
Serious descaling first might be appropriate. Use FlowAid at a high strength concentration for best results in your case.
I've never seen nor heard of how the pump itself is descaled.
That condensation under the black drain accumlulator at the top of your photo is a phenomenon on NPE A, but not much to worry about. Wipe till clean and don't get that juice on an open wound, it hurts !
There are button presses to determine recirculation flow. Best to have a service manual for that, but briefly:
Press diagnostic button once to access the service info display.
Press + to navigate through the user parameters...(A) Flow Rate will be displayed "GPM A 10.2" meaning flow rate is 10.2 gal. per min.
Press reset button once to return to normal operation mode. If there is no button input for 1 hour, then it automatically returns to the normal op mode.