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Navien · Tankless water heater troubleshooting

Water not hot enough or too hot - Navien NPE-2

What is going on

Hot water temperature is lower or higher than expected.

Likely causes

  • Set temperature wrong
  • Cross plumbing between hot and cold lines
  • Temperature lock on
  • Commercial Mode off

Check in this order

  1. Check the set temperature (factory 120 F / 49 C). Range 97-140 F; while a tap is open it can only be changed between 97-110 F.
  2. For not hot enough, check for cross plumbing (e.g. faulty mixing valve) between the hot and cold lines.
  3. If the temperature cannot be changed, front-panel DIP switch 2 (temperature lock) may be ON.
  4. Above 140 F (up to 185 F) requires Commercial Mode: Installer Menu > Parameter 12 (temperature lock must be OFF).
  5. Warning: water at or above 125 F can scald instantly - recommend a mixing valve before raising the setting.

Applies to: Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2

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Source: Navien NPE-A2/S2 User's Information Manual (20049624A), 5.1, p.16; Navien NPE-A2/S2 Installation Manual, 7.3, p.91-92. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.