E110 — Exhaust Blockage / APS Fault
The air pressure switch or exhaust pressure sensor reports abnormal vent pressure — typically a blocked or restricted intake/exhaust.
- Keep using it?
- Limited use only
- DIY difficulty
- Moderate
- Verified against
- navieninc.com ↗
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.
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 replacementAmazon →
Related repair guides
More Navien tankless water heater codes
Frequently asked questions
What does the E110 code mean on a Navien tankless water heater?
The air pressure switch or exhaust pressure sensor reports abnormal vent pressure — typically a blocked or restricted intake/exhaust.
What causes the E110 code on a Navien tankless water heater?
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.
Is it safe to keep using a Navien tankless water heater with a E110 error?
Limited use only. This is rated a serious-severity fault.
How do I fix E110 on a Navien tankless water heater?
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.
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: navieninc.com.