Navien Boiler Error Codes: Causes & Fixes

If your Navien boiler has suddenly stopped working and you’re seeing a fault message on the display, you’re not alone. Navien boiler error codes are designed to help diagnose what’s wrong, but they can look confusing if you’re not a heating engineer. 

This guide breaks down the most common error codes, what they mean, what causes them, and how to fix them safely.

What Are the Most Common Navien Boiler Error Codes?

Below are the most frequently reported Navien boiler error codes in the UK.

Navien error code E003 

The E003 indicates an ignition failure, meaning the boiler attempted to ignite but could not produce a stable flame. This prevents the boiler from heating water or supplying central heating.

Causes

No gas supply or low gas pressure

If the boiler isn’t receiving enough gas, ignition cannot occur. This may happen if the gas meter has been turned off, credit has run out on a prepayment meter, or there’s an issue with the local gas network. Low gas pressure can also occur in cold weather when demand is high.

Air in the gas line

Following maintenance or periods of inactivity, air can become trapped in the gas supply line. This prevents consistent ignition and may require purging by a Gas Safe engineer.

Blocked burner

Dirt, soot, or debris on the burner can disrupt flame formation. A blocked burner reduces combustion efficiency and can cause repeated E003 ignition failures.

Faulty igniter or flame sensor

If the igniter cannot spark or the sensor cannot detect the flame, the boiler will shut down as a safety precaution. These components naturally wear over time and may need replacement.

Frozen or blocked condensate pipe

In UK winters, condensate pipes can freeze outside, backing up moisture into the boiler. This disrupts ignition and is one of the most common seasonal causes of E003.

How to fix error code E003

Try these steps safely:

1. Check that other gas appliances work
2. Reset the boiler using the front control panel
3. Ensure the condensate pipe is not frozen (common in UK winters)
4. Check for visible kinks in the flue (do not dismantle)

Call a Gas Safe registered engineer if:

• the code returns repeatedly
• you smell gas
• ignition components need replacing
  

Navien error code E012 

The E012 error code relates to flame loss, meaning the flame ignites but cannot stay stable during operation.

Causes 

Flue obstruction from debris or weather

Bird nests, leaves, snow, or wind-blown debris can restrict airflow. When exhaust gases cannot escape, the flame becomes unstable and the boiler shuts down.

Poor combustion due to incorrect air–gas mix

If the boiler isn’t getting the correct oxygen balance, the flame becomes weak. This can be caused by faulty calibration, blocked vents, or gas supply inconsistencies.

Moisture in ignition components

Condensation or leaks can accumulate inside the boiler and affect electrical ignition components, causing intermittent loss of flame.

Blocked heat exchanger

Limescale, sludge, or corrosion can restrict water flow and heat transfer, resulting in unstable flame behaviour and triggering E012.

Weak gas supply

If the flame loses strength mid-operation, it suggests fluctuating or inadequate gas delivery, often tied to external supply conditions.

How to fix error code E012

Homeowners can:

• Check flue terminal for obstructions such as leaves or snow
• Reset the boiler after waiting 5 minutes

A heating engineer may:

• adjust combustion
• clean burner assembly
• test gas pressure
• inspect heat exchanger
  

Navien error code E030 

This E030 error code signals a blocked exhaust or flue issue, which can be dangerous because fumes may not be venting safely.

Causes

Blocked or iced flue

A blocked flue prevents exhaust gases from exiting safely. Ice in winter or nesting debris in warmer months can both trigger this code.

Incorrect flue installation

If the flue has been fitted with the wrong gradient, length, or sealing, airflow becomes turbulent and unsafe, leading to an automatic shutdown.

Strong winds causing backdraft

High winds can blow exhaust gases back toward the boiler, disrupting ventilation pressure. This is more common in coastal or exposed locations.

Internal fan failure

The fan ensures proper airflow through the combustion chamber. If the fan slows, sticks, or burns out, the boiler cannot safely operate.

How to fix error code E030

Do NOT attempt to use the boiler until this is resolved.

Steps:

• Inspect outdoor flue terminal visually (do not remove parts)
• Check for ice build-up in freezing weather
• Call a professional if the code persists

This error has safety implications and should be prioritised.

Navien error code E046

The E046 error code refers to low or unstable system water pressure, impacting the heating circuit.

Causes

System leaks in radiators or pipes

Even small leaks reduce water pressure over time. Drips may occur at radiator valves, pipe joints, or under flooring, causing repeated pressure drops.

Recently bled radiators

After bleeding radiators, trapped air escapes and system pressure drops. If the system isn’t topped back up, the boiler detects low pressure.

Faulty pressure sensor

If the sensor sends incorrect readings to the boiler, it may falsely detect low pressure even when the system is correctly filled.

Expansion vessel issues

A failed or deflated expansion vessel causes pressure fluctuations as heating demand changes. This is a common cause in older systems.

How to fix error code E046

Homeowners can:

1. Check pressure gauge (should be around 1.0–1.5 bar)
2. Use filling loop to top up system
3. Reset boiler after repressurising

Call an engineer if:

• pressure drops repeatedly
• water is visible under boiler
• expansion vessel needs recharging

Navien error code E109

The E109 error code indicates a fan or air pressure switch (APS) failure, affecting airflow and combustion safety.

Causes 

Faulty fan motor

If the fan cannot create the required airflow, safe combustion cannot occur. Grinding noises or intermittent running often indicate failure.

Blocked flue

Restricted airflow can trigger both E030 and E109. The APS detects incorrect pressure and shuts the boiler down to prevent unsafe burning.

Damaged APS tubing

Cracked, kinked, or loose tubing prevents the air pressure switch from detecting airflow correctly, leading to false shutdown signals.

Wiring failure

Loose, corroded, or damaged wiring interrupts communication between the fan, APS, and PCB, causing safety lockouts.

How to fix error code E109

Because this affects safe combustion, a Gas Safe engineer must diagnose it.

Possible repairs:

• fan replacement
• APS replacement
• wiring inspection
• flue testing

Navien error code E515

The E515 error code points to a PCB (Printed Circuit Board) communication fault, meaning internal components aren’t communicating properly.

Causes

Loose electrical connectors

Vibration, heat expansion, or poor installation can loosen internal wiring plugs, leading to intermittent PCB communication errors.

Moisture ingress

Humidity, leaks, or condensate issues can interfere with electronic components and cause digital errors or shutdowns.

PCB failure

The PCB is the boiler’s control brain. Component aging, overheating, or electrical surges can lead to permanent failure.

Voltage irregularities

Fluctuations in household electrical supply—often from faulty circuits or storms—disrupt internal communication and trigger E515.

How to fix error code E515

Homeowners should:

• power cycle the boiler
• check for tripped electrics

Engineers may:

• replace PCB
• test voltage supply
• reseat connections
  

FAQs 

1. Can I clear Navien error codes by resetting the boiler?

Sometimes, yes—especially after a power dip or temporary pressure issue. If the code returns, further diagnosis is required.

2. Are Navien boiler error codes different in the UK vs USA?

Yes, UK models may feature different safety standards and code definitions due to Gas Safe regulations and flue rules.

3. Will error codes affect energy efficiency?

Yes—issues like poor combustion or low pressure can increase fuel use and reduce condensing efficiency.

4. Do Navien error codes appear during annual servicing?

Engineers can access historic stored fault logs during servicing, helping predict failures.

5. Can smart thermostats cause Navien boiler error alerts?

Incorrect wiring or incompatible controls can trigger communication-related errors.