E110 Exhaust blockage

What the control is telling you

The control detected a blocked exhaust/air path. Manual action: check exhaust venting. The User's Information Manual adds that a clogged air intake filter also causes code 110.

Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers

Likely causes

• Air intake filter clogged with dust or lint
• Blocked exhaust or intake termination (snow, ice, debris, nests)
• Vent too long or too many elbows
• Condensate backing up into the vent

Test and repair steps

1. Warning: Turn off and unplug the boiler before opening the cover.
2. Remove the air intake filter (top left inside the cabinet), rinse with clean water, dry and refit.
3. Check both terminations are clear and at least 12 in above grade/snow line.
4. Confirm vent length and elbows 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).
5. Check horizontal runs slope up 1/4 in per ft toward the termination and the condensate drain is clear.
6. Check APS voltage readings in Status Info after repairs.

Settings for these units

Installation clearances (indoor) · Navien NHB-H

Bracket gives 5/8 in (16 mm) from the wall; studs at 16 in on centre.

Common vent installs: 36 in above the top and 24 in in front are recommended for service.

Installation clearances (indoor) · Navien NFB-H

Do not install on carpet; indoors only.

Remove the wood pallet and refit the 6 screws to keep the cabinet airtight.

Models that show this code

6 models in Navien NHB-H, Navien NFB-H

Other codes on the same units

• E046 Heat exchanger thermistor fault
• E047 Exhaust thermistor fault
• E060 Dual venturi fault
• E109 Fan motor fault
• E205 Heating supply temperature sensor
• E218 Heating return temperature sensor
• E278 External system supply sensor not detected
• E279 External system return sensor not detected