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Navien · Tankless water heater troubleshooting

Hot water turns cold - Navien NPE-2

What is going on

Water from the hot tap is cold or turns cold and stays cold.

Likely causes

  • Clogged inlet filter
  • Flow below the 0.5 GPM minimum
  • Error code
  • Missing check valve on an external recirculation return

Check in this order

  1. Clean the cold water inlet filter.
  2. Open the tap fully - at least 0.5 GPM must flow to fire the unit.
  3. Check the display for an error code.
  4. With an external recirculation system, make sure a check valve is on the recirculation return line.
  5. Check gas pressure at max fire (3.5-10.5 in. WC NG, 8.0-13 in. WC LP) if it happens at high demand.

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 Solving Basic Problems, p.16. 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.