HVACopediaNavien · Combi boiler
E762 Vent pipe not fully inserted (VID)
What the control is telling you
The Vent Installation Detector switch in the exhaust collar does not detect a fully inserted vent pipe; the boiler will not run. NFC-H manual lists the reset type as: Auto reset.
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
- Vent pipe not pushed fully 2-3/4 in (70 mm) into the collar
- Wrong pipe size, deformed pipe, misaligned or moving pipe
- Street elbow used at the collar
Test and repair steps
- Warning: carbon monoxide hazard - do not run the boiler with a loose vent connection.
- Mark the pipe 2-3/4 in (70 mm) from the end, cut square (90°) and deburr, lubricate with water (not grease) and push in with a twist until the mark disappears.
- Use the correct 2 in pipe at the collar; never start the run with a street elbow - use a straight length.
- Tighten the collar clamp (8 mm socket) and support the pipe so it cannot move vertically.
- Bubble-test the exhaust joints with the boiler running.
- Note the VID does not detect leaks or separation further along the vent; inspect the whole run.
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
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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.
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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.