HVACopediaNavien · Combi boiler
E302 Low water pressure (internal LWCO)
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
| Side | Minimum |
|---|---|
| Top | 9 in (229 mm) |
| Back | 0.5 in (13 mm) |
| Front | 4 in (100 mm) |
| Sides | 3 in (76 mm) |
| Bottom | 12 in (300 mm) |
Indoor wall-hung only; ambient must stay above 32°F (0°C).
Do not install on carpet; leave room for service.
Water quality limits (DHW and system fill) · Navien NFC-H
| Contaminant | Max allowed |
|---|---|
| Total hardness | 200 mg/l (12 grains/gallon) |
| Aluminum | 0.05 to 0.2 mg/l |
| Chloride | 250 mg/l |
| Copper | 1.0 mg/l |
| Iron | 0.3 mg/l |
| Manganese | 0.05 mg/l |
| pH | 6.5 to 8.5 |
| Sulfate | 250 mg/l (DHW table); 205 mg/l (fill table) |
| Total dissolved solids | 500 mg/l |
| Zinc | 5 mg/l |
| Chlorine (fill water) | 4 mg/l |
Manual shows sulfate 250 mg/l on p.26 and 205 mg/l on p.33.
Models that show this code
2 models in Navien NFC-H
Other codes on the same units
- E205 Heating supply temperature sensor fault
- E218 Heating return temperature sensor fault
- E278 External (system) supply sensor not detected
- E279 External (system) return sensor not detected
- E351 Auto feeder (make-up water) valve fault
- E352 High water pressure
- E353 Water pressure sensor fault
- E407 DHW outlet temperature sensor fault
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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.