Navien Tankless Water Heater E110 — Exhaust Blockage / APS Fault
Navien Tankless Water Heater · Error code E110
What E110 Means
The air pressure switch or exhaust pressure sensor reports abnormal vent pressure — typically a blocked or restricted intake/exhaust.
Symptoms
- E110 on display
- Unit will not fire
- Slow start or repeated lockouts
- Visible condensate at vent
Common Causes
Bird/insect nests at termination, sagging PVC trapping condensate, or excessive vent length.
Lint, snow, or debris at intake termination.
Pressure-sense tube to the switch dislodged or pinched.
Switch reads wrong or sensor drifted.
Too many elbows or undersized pipe exceeding the allowed equivalent length.
How to Fix It
- Inspect intake and exhaust terminations outdoors — clear nests, snow, lint screens.
- Walk the vent run looking for sags that pool condensate; correct slope (1/4" per ft back to unit).
- Open the cover and inspect the APS pressure tubing — reseat or replace if cracked.
- Test the air pressure switch / sensor per service manual; replace if out of spec.
- Verify vent length and elbow count are within the model's published limits.
- If everything passes, replace the APS or pressure sensor.
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.
More Navien Tankless Water Heater Codes
Verified against manufacturer documentation: navieninc.com
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.