HVACopediaNavien · Combi boiler
E788 Incorrect gas type setting
What the control is telling you
The gas type setting does not match the PCB DIP switch. NFC-H lists it as abnormal gas setting, cleared through the Start-up Wizard. NFC-H manual lists the reset type as: Manual reset (Start-up Wizard).
Applies to: Navien fire-tube combi boilers, NFC-H series (NFC-250/200H, NFC-250/175H) and NCB-H combi boilers (NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H)
Likely causes
- Start-up Wizard gas type not matching DIP SW2 #1
- Wrong DIP switch setting
Test and repair steps
- Confirm which gas is supplied and set the PCB DIP switch to suit: SW2 #1 OFF for NG, ON for LP.
- Re-run the Start-up Wizard and choose the same gas type.
- Code keeps returning? Phone Navien Technical Support, 1-800-519-8794.
Settings for these units
Minimum installation clearances (indoor) · Navien NCB-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 NCB-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 |
Scale damage from poor water is not covered by warranty.
Manual shows sulfate 250 mg/l on p.23 and 205 mg/l on p.29 - check local guidance.
- Minimum installation clearances (indoor) · Navien NFC-H
- Water quality limits (DHW and system fill) · Navien NFC-H
Models that show this code
7 models in Navien NCB-H, Navien NFC-H
Other codes on the same units
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Navien NCB-H Installation & Operation Manual, 11.7 Understanding Error Codes, p.129-130; Navien NFC-H Installation Manual, 11.7 Understanding Error Codes, p.127-128. 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.