Navien NPE-A2 condensing tankless (ComfortFlow): quick sheet

Covers: Navien NPE-180A2, NPE-210A2 and NPE-240A2 (A2 = built-in buffer tank and recirculation pump, 'ComfortFlow'); the NPE-S2 models (150S2-240S2) are the same generation without ComfortFlow. Earlier NPE-A (first generation) units differ in controls.

Single sourceBrands: Navien6 components

A very common plumber-installed condensing tankless, recognized by the EZNav multi-line display and 2 in PVC venting. The A2's built-in buffer tank and recirculation pump reduce cold-water sandwich and can recirculate through a dedicated return or, with the NaviCirc valve, through existing supply lines.

Safety first

Gas, burner, fan and venting are blocked: refer to a licensed gas technician.
120 V inside: disconnect power before opening.
LP conversion must be done by a qualified service agency.

How it works

A flow sensor tells the board water is moving; the board fires and modulates the burner across a turndown of up to 15:1 to hold set temperature.

Dual stainless steel heat exchangers (primary and condensing secondary) recover flue heat; condensate drains and should be neutralized.

ComfortFlow: an internal buffer tank smooths outlet temperature and an internal pump drives recirculation, either through an external return line or through the cold line using a NaviCirc crossover valve.

Up to 32 units can be cascaded (Ready-Link) and up to 12 common-vented. NaviLink adds Wi-Fi control.

Components & tests

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Large stainless refrigerator set flush between kitchen cabinets by Alex Qian, Pexels License

Diagnostic guides for this appliance

Guide · Water Heater

Heat-pump (hybrid) water heater: slow recovery, noise, errors

Hybrids need enough room air and a clean air filter, a working condensate drain and the right mode. Many complaints are mode settings or a dirty filter. Refrigerant faults are sealed-system work.

5 steps ~60 minmoderate

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Tankless water heater descaling (flush)

Scale insulates the heat exchanger, causing overheat codes and fluctuating temperature. Flush with a pump and descaling solution through the isolation valves.

5 steps ~75 mineasy

Guide · Water Heater

Hot water recirculation pump problems

Check timer/settings, check valves, air in the loop and the pump itself. On tankless units with built-in pumps, a recirculation code may point to air or a leak in the loop.

5 steps ~60 minmoderate

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Rinnai RU / RUR (SENSEI) condensing tankless: quick sheet

Rinnai condensing residential tankless: RU-series (RU199iN/eN, RU180, RU160, RU130; indoor 'i' and outdoor 'e'), RUR models with built-in recirculation. Older non-condensing RL / V-series and RE models differ. Rinnai serial numbers encode year then month in the first four digits.

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