5.12. 21ErrorError occurrence conditions and check items.DescriptionError21EHeat exchangerinputtemperaturesensor openCheck itemsIf an error (open: -10Ȕor lower) in the heat exchanger input temperature sensoris detected, the system displays the 21E error message on the remote controllerand the PCB.The boiler maintains the Safety-Shutdown status.1. Check if the heat exchanger input temperature sensor connector is wet due toany reason, including leakage.2. Replace the defected heat exchanger input temperature sensor.3. Replace the PCB.©Navien America Inc. 2010 NR/NP series service Manual95Version 2.0Check methodErrorDefectivesensorOther troubleDefectivetemperature sensorconnectorTemperaturesensorDefectivePCB<Heat exchanger input temperature sensor /connector, Black 2P>eck if the hot water temperature sensor is open>Error type : MΩ OpenCheck if the temperature sensor is open and if the connector isconnected properly.Check the resistance of the temperature sensor.(Defective if it is 30๐or higher) Replace the temperature sensor if the resistance value is abnormal. Check the temperature displayed on the PCB. (C.10.0ȥ10.0Ȕ).If the trouble continues despite the checking of above items,replace the PCB.CauseCheck method
