Navien · Combi boiler

E302 Low water pressure (internal LWCO)

High severity Navien NFC-H

What the control is telling you

NFC-H only: the built-in pressure-type low water cutoff sees insufficient water in the boiler (minimum operating pressure 6 psi by default). Needs a manual reset. This code is mentioned in the LWCO section but is not in the manual's error code table.

Applies to: Navien NFC-H fire-tube combi boilers (NFC-250/175H, 250/200H)

Likely causes

Low system pressure / leak
Make-up water supply closed
Auto-fill not working

Test and repair steps

Check system pressure (Status Information > 16. Water Pressure) and look for leaks or a discharging relief valve.
Make sure make-up water to the boiler is open and the Auto-Fill Pressure parameter is set correctly (12-50 psi, default 12 psi).
Refill and purge air.
Reset from the front panel by pressing the Back button, then confirm the code clears.
Code keeps returning? Phone Navien Technical Support, 1-800-519-8794.

Settings for these units

Minimum installation clearances (indoor) · Navien NFC-H
Water quality limits (DHW and system fill) · Navien NFC-H

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Source: Navien NFC-H Installation Manual, 3.1 Internal LWCO note, p.23. 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.