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Navien · Boiler

E302 Low water pressure

High severity Navien NHB-HNavien NFB-H

What the control is telling you

The built-in pressure-sensing low water cutoff saw system pressure below the low limit (default 6 psi). Needs a manual reset after the cause is fixed.

Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers

Likely causes

  • System pressure too low (leak, relief valve discharge, not filled)
  • Air in system
  • Expansion tank problem
  • Low Sys Pressure parameter set too high

Test and repair steps

  1. Read Water Press in Status Info and check the system gauge.
  2. Refill to the design pressure (typical cold fill 12 psi for residential); NHB-H operates at 12-30 psi.
  3. Find and repair leaks; constant make-up water damages the heat exchanger.
  4. Check the expansion tank charge and size and the relief valve for discharge.
  5. Check parameter 16 Low Sys Pressure (range 4-17 psi, default 6 psi).
  6. Reset the boiler with the Back button once pressure is restored.

Settings for these units

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Source: Navien NHB-H Installation and Operation Manual, 11.14 Understanding Error Codes, p.119; Navien NFB-H Installation Manual, 11.7 Understanding Error Codes, p.116; NHB-H User's Information Manual (V1.0 Apr 2024), 5.2, p.24. Summarized in our own words; check the original manual for your model.

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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.