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

Covers: 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.

Single sourceBrands: Rinnai7 components

The most common condensing tankless in US homes. Recognize it by the Rinnai front cover, 3/4 in gas and water connections, a 1/2 in condensate drain and a digital controller. Gas valve, burner and venting work is blocked; techs handle water-side, electrical and diagnostics.

Safety first

Gas valve, burner, combustion fan and venting are blocked: refer to a licensed gas technician; gas odor = leave and call the utility.
120 V inside the cabinet: disconnect power before opening.
Condensate is acidic: wear gloves and eye protection.

How it works

When a fixture opens, the flow sensor detects flow above the activation threshold; the board runs the combustion fan, ignites and modulates the burner (RU199iN: 15,000 to 199,000 BTU/h) to hold set temperature.

Primary and secondary heat exchangers recover flue heat; the condensate from the secondary exchanger drains through the 1/2 in NPT connection, usually through a neutralizer.

Faults show as a two-digit code on the controller; 'LC' indicates scale build-up and prompts a descale flush.

RUR models and recirculation-capable units can run a recirculation program; Wi-Fi is available through Rinnai's module.

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

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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.

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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

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

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.

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