HVACopediaNavien · Combi boiler
E110 Exhaust blockage / abnormal air pressure (APS)
What the control is telling you
The air pressure sensor sees a blocked exhaust or intake. The user manual notes a clogged air intake filter will stop the boiler with this code. NFC-H manual lists the reset type as: Manual 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
- Blocked exhaust pipe or termination (snow, ice, debris, nests)
- Clogged air intake filter
- Vent too long or too many elbows
- Condensate backing up in the vent/trap
Test and repair steps
- Make sure the exhaust pipe and termination are free of obstructions (the manual's listed remedy).
- Clean the air intake filter; the user manual recommends cleaning it every 3-4 months.
- Check vent length 2 in max 65 ft with up to 6 elbows; 3 in max 150 ft with up to 8 elbows (90° elbow = 8 ft on 2 in, 5 ft on 3 in).
- Check the condensate trap is filled and drains freely.
- Compare Status Information 20. Fan Target APS with 21. Fan Current APS.
- 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 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
- E046 Heat exchanger thermistor / overheat sensor fault
- E047 Exhaust thermistor fault
- E060 Dual venturi fault
- E109 Fan motor fault
- 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
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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.
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.