Navien E110 Error Code — What It Means
The E110 error code on a Navien tankless water heater indicates abnormal air pressure or a combustion air and exhaust flow fault. The unit has detected that it cannot draw enough combustion air or vent exhaust gases properly, so it shuts down to prevent unsafe operation. This is an airflow proving failure, not a simple overheating alarm.
In most field cases, the fault comes from something blocking the intake or exhaust path, a dirty internal air filter that restricts airflow, or a clogged condensate drain that upsets the pressure balance inside the unit. Less commonly, the air pressure sensor itself or an internal component has failed.
Common Causes
- Blocked intake or exhaust vent terminations Snow, ice, leaves, dirt, debris, or bird nests can block the outdoor vent pipes and prevent proper airflow through the system.
- Dirty or clogged internal air intake filter Dust and lint accumulate on the filter inside the unit, restricting combustion air and triggering the pressure fault.
- Condensate trap or drain line restriction Sediment, sludge, or slow drainage in the condensate system can upset airflow proving conditions and cause the E110 code.
- Faulty air pressure sensor or switch If all airflow paths are clear but the code returns, the pressure sensing component or its wiring may have failed.
- Heat exchanger restriction or contamination In less common cases, buildup or blockage inside the heat exchanger itself can restrict airflow enough to trip the fault.
Step-by-Step Fix
- Turn off power to the unit at the circuit breaker or service switch and let the heater cool before you open any covers or inspect components.
- Inspect the outdoor intake and exhaust vent terminations for blockage from snow, ice, leaves, nests, or other debris and clear any obstructions you find.
- Remove the front cover of the tankless unit and locate the internal air intake filter, pull it out, wash it thoroughly with water, dry it completely, and reinstall it in the correct orientation.
- Check the condensate trap and drain line for sediment, sludge, or standing water that is draining slowly, and clean the trap and flush the drain if restricted.
- Restore power and run a hot water tap to test the heater and confirm the E110 code has cleared and the unit fires normally.
- If the code returns after all airflow and drain checks are complete, the air pressure sensor, wiring, or heat exchanger condition should be evaluated by a qualified technician.
- Document your findings and keep a record of when the filter was last cleaned to establish a maintenance schedule going forward.
Parts Often Needed
| Part | Notes |
|---|---|
| Navien air intake filter | Amazon | Washable filter inside the unit that keeps combustion air clean. Match your model number. |
| Air pressure sensor / air pressure switch | Amazon | Senses airflow proving. Replace if filter and vents are clean but code persists. Verify part number for your exact model. |
| Condensate trap assembly | Amazon | Replace if the trap is cracked, corroded, or cannot be cleaned effectively. |
When to Call a Pro
Call a qualified Navien service technician if the E110 code returns after you have cleaned the air filter, cleared the vents, and checked the condensate drain. At that point the fault is likely internal, involving the air pressure sensor, wiring, control board, or heat exchanger condition. These components require diagnostic tools, manufacturer training, and access to genuine replacement parts. If you are not comfortable removing covers, working around gas connections, or handling electrical components, call for service from the start rather than attempting the repair yourself.