Jul 30,  · The Navien tankless water heater error code e comes up due to a pump error in majority of the cases. Apart from that, the flow sensor or the PCB being defective can also Missing: Pdf. 26 rows · Find the common Navien fault codes and their descriptions for combi and system boilers. Learn how to reset the boiler or contact an engineer for some g: Pdf. Find brochures, manuals, guides, labels, specs, drawings, revits & certificates for Navien NPEA condensing tankless water g: Error Codes.