Navien-Recommended Water Treatment Installation Sequence
Navien's installation team recommends the following supply line sequence for NPE and NCB installations in hard water areas: main supply -> PRV (if supply pressure above 80 PSI) -> sediment pre-filter (25-micron) -> water softener (bypass valve required) -> cold supply to Navien. The 25-micron pre-filter is critical for well water applications -- particulate matter that bypasses the softener resin tank can damage Navien's inlet flow sensor. Use a Pentek sediment filter housing ($30--$50 at plumbing supply houses) with quarterly filter element replacement.
Navien and Water Softener Plumbing Bypass Configuration
Navien's installation guide requires that the water softener have a three-valve bypass assembly so the softener can be isolated for service without interrupting hot water supply. During softener service or resin replacement, set the softener to bypass, and Navien will operate on untreated water temporarily. Limit bypass operation to less than 48 hours in hard water areas above 12 GPG -- brief bypass exposure does not cause permanent heat exchanger damage, but extended bypass in very hard water can initiate scale nucleation sites that subsequent soft water does not remove.