Navien Bypass Mixing valve error and knocking sound

carne_asada

I have a Navien NPE 210S Tankless water heater that has started marking a knocking sound at the end of the heating cycle when the unit goes back to the standby mode. The unit is also throwing a 445 Bypass mixing valve error. I still have hot water and there are no leaks.

The part is easy enough to replace but I wanted to ask if there is anything else I should check before I replace the mixing valve.

Thanks!

Larry Weingarten

Hi @carne_asada , Do you know what the static water pressure is and, are there any valves in place that would prevent backflow? Also, it might be interesting to put a pressure gauge close to the heater and see if the pressure jumps when the heater is making that noise.

Yours, Larry

carne_asada

Hi @Larry Weingarten ,

The cold water supply pressure seems normal ( I haven't tested) but does occasionally dip depending on building usage.

I don't know if there is a backflow valve (there is likely one for the whole building -nothing in the unit) - the unit is a 4th floor apartment serviced by a booster pump for the building.

I do hear the boiler sometimes adjust (to what I assume) is a dip/increase on the cold pressure when I use just cold water or the building supply pressure changes (knocking also happens during these adjustments) The knocking sound I am hearing is consistent on every end of cycle and during these non-ignition adjustments.

One more piece of info - there was a building wide power outage a few weeks ago where water pressure dropped due to the booster pump going down (boiler also was not powered up during this time).

Thanks!