HVACopedia

Navien · Boiler

E784 Zone controller communication fault

Medium severity Navien NHB-HNavien NFB-H

What the control is telling you

Lost communication with the Navien zone controller. Manual action: check wiring and settings.

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

Likely causes

  • Zone controller wiring loose or wrong
  • Navien zone cont. setting does not match the installation

Test and repair steps

  1. Check the wiring between the boiler and the Navien zone controller.
  2. Confirm Space Htg Operation > 5. Navien zone cont. is Enabled only when a Navien zone controller is installed.
  3. Check zone controller power and settings.

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.

Homeowner looking at this code? See what it means for you and when to call a technician.

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.