E110 — Exhaust Blockage / APS Fault

How to fix it

1. Inspect intake and exhaust terminations outdoors — clear nests, snow, lint screens.
2. Walk the vent run looking for sags that pool condensate; correct slope (1/4" per ft back to unit).
3. Open the cover and inspect the APS pressure tubing — reseat or replace if cracked.
4. Test the air pressure switch / sensor per service manual; replace if out of spec.
5. Verify vent length and elbow count are within the model's published limits.
6. If everything passes, replace the APS or pressure sensor.

Why it happens

Typical signs: E110 on display · Unit will not fire · Slow start or repeated lockouts · Visible condensate at vent

• Blocked or sagging exhaust Bird/insect nests at termination, sagging PVC trapping condensate, or excessive vent length.
• Blocked intake Lint, snow, or debris at intake termination.
• Disconnected or kinked APS tubing Pressure-sense tube to the switch dislodged or pinched.
• Failed air pressure switch / pressure sensor Switch reads wrong or sensor drifted.
• Improper venting Too many elbows or undersized pipe exceeding the allowed equivalent length.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

• Navien air pressure switch Common replacement
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