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Navien · Boiler

E352 High water pressure

High severity Navien NHB-HNavien NFB-H

What the control is telling you

System pressure is above the high limit. Manual action: check water pressure.

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

Likely causes

  • Expansion tank waterlogged, undersized or isolated
  • Fill/pressure reducing valve letting by
  • System overfilled

Test and repair steps

  1. Read Water Press in Status Info and compare with the system gauge.
  2. Check the expansion tank charge and size and that it cannot be isolated from the boiler.
  3. Check the pressure reducing / make-up valve is not over-pressurizing the system.
  4. NHB-H system pressure 12-30 psi with a 30 psi relief valve. NFB-H: 12-80 psi; parameter 17 High Sys Pressure (40-80 psi, default 50 psi) should suit the relief valve rating.
  5. Drain to the correct pressure and retest.

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.