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Navien · Boiler troubleshooting

No space heat - Navien NHB-H / NFB-H

What is going on

Thermostat calls for heat but the boiler does not heat the zones and shows no error code.

Likely causes

  • Set temperature too low or outdoor reset / WWSD holding heat off
  • Boiler off, no power or in standby
  • Boiler busy with indirect DHW (DHW priority)
  • Thermostat DIP switch or zone settings wrong
  • Pump or zone valve not powered

Check in this order

  1. Check the space heating set temperature; with outdoor reset on, check the outdoor temperature against WWSD (default OFF) and the curve.
  2. Make sure the boiler has 120 V power and is turned on with the Power button.
  3. If the indirect tank is calling, space heating waits up to the DHW Priority Time (default 30 min).
  4. Check DIP SW2 #7: OFF = thermostat used, ON = unused (continuous operation).
  5. Check Input/Output Status is the thermostat input seen, and are the boiler pump, zone pumps or zone valves energized?
  6. Run Test Mode for the pumps and zone valves to confirm they operate; check Zone Settings (pump vs valve system) match the install.
  7. Check Error History for codes that cleared on their own.
  8. Press Back to reset. If still no heat, call Navien technical support 1-800-519-8794.

Applies to: Navien NHB-H and NFB-H condensing boilers

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Source: Navien NHB-H User's Information Manual (V1.0 Apr 2024), 5.1 Solving Basic Problems p.23; NHB-H Installation and Operation Manual 6.2 p.68, 11.8-11.9 p.104-108, 11.13 p.110-117. 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.