Navien E110 Fault Code: Abnormal Air Pressure / Flue Restriction
The E110 code means the Navien unit's control board has detected that air pressure within the combustion system is outside the acceptable operating range. A pressure switch continuously monitors the differential between ambient air and the combustion chamber — when it senses a restriction or anomaly in airflow, it triggers E110 and locks the unit out as a precaution. While the lockout is active, the gas valve is closed and the burner is not firing, so there is no active combustion and no risk of carbon monoxide production from the unit in this state.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
What does the Navien E110 fault code mean?
The E110 code means the Navien unit's control board has detected that air pressure within the combustion system is outside the acceptable operating range. A pressure switch continuously monitors the differential between ambient air and the combustion chamber — when it senses a restriction or anomaly in airflow, it triggers E110 and locks the unit out as a precaution. While the lockout is active, the gas valve is closed and the burner is not firing, so there is no active combustion and no risk of carbon monoxide production from the unit in this state.
Common causes
- Blocked or dirty air intake filter Common
Dust, leaves, insects, and other external debris gradually accumulate on the mesh air intake filter. Once restricted enough, the filter reduces airflow into the combustion chamber, causing the pressure switch to detect an anomaly and trigger E110. This is the most frequent single cause and is straightforward to address.
- Blocked or obstructed flue terminal Common
The external flue terminal can become partially or fully blocked by bird nests, leaves, ice, or compacted debris. Strong winds or heavy snowfall can also temporarily restrict the terminal. Any significant restriction to exhaust gas escape will cause abnormal pressure readings inside the combustion system.
- Frozen or blocked condensate drain Sometimes
Navien condensing units produce condensate as a by-product of extracting heat from exhaust gases. If the condensate trap or drain pipe freezes during cold UK winters, or becomes blocked by scale or debris, the resulting pressure imbalance inside the flue circuit can trigger E110. Lagging exposed pipes before winter reduces this risk considerably.
- Faulty or sticking inducer (fan) motor Sometimes
The inducer fan draws combustion air through the heat exchanger and pushes exhaust gases out through the flue. If the fan motor begins to fail, runs slower than expected, or seizes, it cannot maintain the correct differential pressure, causing E110 to appear even when the flue and filter are clear.
- Failed air pressure switch (APS) Rare
The pressure switch itself can develop a fault — either through membrane failure, a blocked sensing port, or an electrical issue. A faulty APS may report abnormal pressure even when airflow is perfectly adequate. This is typically diagnosed after other causes have been ruled out.
How to fix it
- Check your gas supply is on DIY safe
Before anything else, confirm that the gas supply to the property is active. Check that other gas appliances (e.g. hob or cooker) are working normally. If there is no gas supply at all, contact your gas supplier rather than investigating the boiler further.
- Inspect the external flue terminal from outside DIY safe
Go outside and visually inspect the flue terminal on the external wall or roof. Look for obvious blockages such as a bird nest, accumulated leaves, ice, or debris covering the opening. Do not attempt to dismantle or modify the flue terminal yourself. If you spot a clear external blockage you can safely reach (e.g. leaves at ground level), remove it carefully. If you suspect a bird nest or internal flue blockage, this requires a Gas Safe engineer.
- Clean the air intake filter DIY safe
Locate the air intake filter on the unit — typically behind a removable front panel. Remove the filter mesh carefully, rinse it under warm running water, and allow it to dry fully before refitting. Avoid using detergents or solvents. Navien recommends cleaning this filter every three to four months, or more frequently if the unit is in an area with higher airborne dust or debris. Refit the filter securely before attempting a reset.
- Thaw a frozen condensate pipe (winter months only) DIY safe
If temperatures are at or below freezing and the condensate drain pipe runs externally, it may have frozen solid. Pour warm (not boiling) water along the exposed section of the pipe to gently thaw the ice. Once thawed, insulate the pipe with foam lagging to reduce the risk of it freezing again. This is particularly relevant to UK winters where overnight temperatures regularly drop below 0°C.
- Reset the unit DIY safe
Once you have completed the checks above, reset the Navien unit using the controls on the front panel (typically the Back or Reset button, depending on your model). Allow the unit to attempt ignition and observe whether E110 returns. If the fault clears and does not return, monitor the unit over the next few days. Do not reset the unit more than two or three times in quick succession — repeated failed ignition attempts without resolving the underlying fault will not help and may mask a more serious issue.
- Call a Gas Safe registered engineer if E110 persists Gas Safe engineer
If the fault code returns after completing all the homeowner checks above, the cause is likely an internal component issue — a faulty inducer fan, failed air pressure switch, or a flue obstruction that cannot be cleared from the outside. A Gas Safe registered engineer can carry out a full flue integrity check, test the pressure switch and fan motor with diagnostic equipment, and replace any faulty components. Do not continue resetting the unit repeatedly or attempt to bypass the fault yourself. All gas-side and internal combustion system work must be carried out by a Gas Safe registered engineer — uncertified work is illegal in the UK and will invalidate your insurance and any remaining manufacturer warranty.
Parts you may need
- Air pressure switch (APS) · from £45
- Inducer fan motor assembly · from £120
- Air intake filter mesh · from £15
- Condensate trap assembly · from £35
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£320, depending on the underlying cause.
Frequently asked questions
Is it safe to leave my Navien unit while E110 is showing?
Yes, it is safe in the immediate sense — when E110 is active, the unit has locked out and the gas valve is closed, so there is no active combustion taking place and no carbon monoxide being produced by the boiler. However, you will have no heating or hot water until the fault is resolved, so it is worth addressing promptly, especially in winter.
How often should I clean the Navien air intake filter to prevent E110?
As a general rule, clean the air intake filter every three to four months. If your property is in an area with higher levels of airborne dust, pollen, or debris — such as near farmland or a busy road — check it more frequently, perhaps monthly. A quick visual inspection takes only a few minutes and can prevent an inconvenient lockout.
Can a strong wind outside cause E110 on a Navien boiler?
Yes, it can. High winds blowing directly at the flue terminal can temporarily interfere with exhaust gas expulsion and cause the pressure switch to detect abnormal conditions. If E110 appears only during very windy weather and clears on its own after a reset, the flue terminal position or the absence of a suitable wind-deflector cowl may be contributing. Mention this pattern to your Gas Safe engineer, as fitting a different terminal type can help in exposed locations.
The engineer mentioned replacing the inducer fan — is that expensive?
An inducer fan motor replacement on a Navien unit typically costs between £180 and £320 all-in, including parts and labour. The fan motor part itself is usually around £100–£130, with the remainder covering the engineer's time. In some cases, the full fan assembly including the housing needs replacement, which can push costs slightly higher. A heat exchanger replacement — a less common but more costly repair — can cost significantly more, but that would not typically be the diagnosis for E110 alone.