Navien Boiler Error Codes: Causes & Fixes
Navien boiler error codes are clear diagnostic alerts displayed on your NCB or LCB series combi or system boiler when the unit detects a problem.
The most common Navien boiler error codes UK homeowners and landlords encounter are E001 (heat exchanger overheating), E003 (ignition failure), E004 (false flame detection), E012 (flame loss), E016 (secondary overheat), E030 (abnormal exhaust temperature), E109 (fan fault) and E110 (exhaust blockage).
These usually stem from simple issues like low gas pressure, frozen condensate pipes, sensor faults or circulation problems and can often be cleared with a reset or quick check.
This guide provides a quick-reference table plus detailed explanations, causes and safe step-by-step fixes so you can get your heating and hot water back on track confidently.
Navien Boiler Error Codes: Quick Overview
The table below summarises the most frequent Navien boiler error codes, what they mean and the typical trigger. Many are easy to resolve at home while others need a Gas Safe engineer.
| Error Code | Meaning | Brief Cause |
| E001 | Heat exchanger overheating | Pump failure, low flow or blockage |
| E003 | Ignition failure | Gas supply, electrodes or valve |
| E004 | False flame detection | Flame sensor fault |
| E012 | Flame loss during operation | Gas pressure drop or condensate freeze |
| E016 | Secondary heat exchanger overheat | Limescale or poor circulation |
| E030 | Exhaust temperature too high | Blocked flue or fan issue |
| E109 | Fan speed error | Dirty or faulty fan |
| E110 | Exhaust blockage or pressure fault | Debris, bird nest or flue issue |
| E205 | Supply thermistor short circuit | Wiring or sensor damage |
These codes help you act quickly. Most Navien boilers will lock out safely until the issue is addressed.
E001 Error Code
The E001 error code on a Navien boiler means the primary heat exchanger has overheated, triggering a safety shutdown to protect the unit.
What Causes the E001 Error Code
This is often due to a failing circulation pump, airlocks, closed radiator valves, sludge buildup or low system pressure stopping proper water flow through the heat exchanger.
How to Fix
- Check all radiator valves are open and bleed any trapped air.
- Verify the boiler pressure is 1–1.5 bar and top up using the filling loop if low.
- Power off at the isolator for 5 minutes, then restart and reset the boiler.
- If the code returns, a Gas Safe engineer must test the pump and flush the system.
E003 Error Code
The E003 error code on a Navien boiler indicates ignition failure. The burner sparks but cannot establish or sustain a flame.
What Causes the E003 Error Code
Common causes include no gas supply, dirty or worn ignition electrodes, low gas pressure, a faulty gas valve or a blocked condensate pipe in winter.
How to Fix
- Confirm other gas appliances (hob/cooker) work; if not, contact your supplier.
- Ensure the gas meter valve is fully open.
- Thaw any frozen condensate pipe gently with warm water if it’s cold outside.
- Reset the boiler; if E003 returns, call a Gas Safe engineer for electrode cleaning or gas-valve checks.
If your Navien boiler keeps showing ignition or flame-related codes, a professional boiler service can diagnose and resolve it before it becomes a costly breakdown.
E004 Error Code
The E004 error code means the boiler detects a flame when it should not. This is a false flame signal that locks the system out for safety.
What Causes the E004 Error Code
This is usually a faulty flame rod/sensor, wiring issue or residual flame from poor combustion in previous cycles.
How to Fix
- Power cycle the boiler fully (off at isolator for 5 minutes).
- Reset and attempt ignition again.
- If the code persists, the flame sensor needs professional cleaning or replacement – only a Gas Safe engineer can safely access it.
E012 Error Code
The E012 error code on a Navien boiler signals flame loss during normal operation. The flame lights but then extinguishes unexpectedly.
What Causes the E012 Error Code
Typical triggers are dropping gas pressure, frozen condensate pipe, partial flue blockage or a failing gas valve.
How to Fix
- Check gas supply and meter valve.
- Thaw the condensate pipe if frozen.
- Reset the boiler and monitor.
- Persistent E012 requires an engineer to check gas pressure and combustion.
E016 Error Code
The E016 error code indicates the secondary heat exchanger (plate) has overheated, common in combi models.
What Causes the E016 Error Code
Limescale buildup in hard-water areas, sludge migration or restricted hot-water flow causes the exchanger to overheat.
How to Fix
- Note if hot water goes cold quickly. This is a classic sign.
- Avoid DIY descaling chemicals.
- Book a Gas Safe engineer for a power flush and plate heat-exchanger clean.
E030 Error Code
The E030 error code means the exhaust gas temperature is abnormally high, indicating poor flue performance.
What Causes the E030 Error Code
The typical causes include a blocked flue terminal, bird nest, fan issues or restricted airflow.
How to Fix
- Visually inspect the flue outlet for debris (from outside only).
- Reset the boiler.
- Any flue work must be carried out by a Gas Safe engineer.
E109 Error Code
The E109 error code signals the fan is not reaching the correct speed.
What Causes the E109 Error Code
This fault is caused by dust, debris or motor wear on the fan assembly.
How to Fix
- Reset and listen for fan operation.
- If silent or noisy, only an engineer can test and replace the fan safely.
E110 Error Code
The E110 error code indicates an exhaust or air-pressure fault, often a blockage.
What Causes the E110 Error Code
Debris in the flue, condensate backup or fan-related pressure issues usually causes this problem.
How to Fix
- Check and clear visible external flue blockages.
- Reset the boiler.
- Professional flue inspection and clearing is required if the code returns.
Getting your boiler serviced annually catches sensor wear, fan issues and early limescale before they trigger repeated Navien boiler error codes and keeps your warranty valid.
Protect Your Boiler Year-Round with Service and Cover Options
At PlusHeat, we make it simple to keep your boiler safe, efficient, and reliable across the UK. If you’re due for a routine check-up, tune-up, or want to prevent future Navien boiler error codes, start with our flexible boiler service plans that focus on proactive maintenance and early fault detection.
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Frequently Asked Questions
Do Navien error codes reset automatically after fixing the cause?
Most codes clear after a successful reset once the underlying issue is resolved, but persistent codes like E001 or E016 will lock out again until professionally repaired.
Can I use a third-party app or Wi-Fi kit to view Navien error codes remotely?
Yes. Navien’s NaviLink or compatible smart controls let you monitor error codes from your phone, but you still need a Gas Safe engineer for any gas-related fixes.
Are Navien boiler error codes the same on NCB and LCB models?
The core E0xx codes are identical across the NCB and LCB ranges in the UK, making troubleshooting consistent regardless of whether you have a combi or system boiler.
Will ignoring a Navien E030 exhaust temperature code damage my boiler?
Yes, prolonged high exhaust temperatures can damage the heat exchanger and flue seals. Always address it promptly to avoid expensive repairs.
How often should I expect to see Navien boiler error codes if my system is well maintained?
With annual servicing, most homeowners see error codes only rarely. Repeated codes usually signal that a service or minor repair is overdue.
