Navien Error Code E004

What Does E004 Mean?

Error code E004 indicates false flame detection - the boiler's flame sensor is detecting a flame signal even when the gas valve should be closed.

This is a safety lockout that prevents the boiler from operating until the issue is resolved.

Why This Is Serious

False flame detection can indicate:

• Electrical interference affecting the flame sensor
• A faulty flame sensor sending incorrect signals
• Water or moisture on electrical components
• A stuck or leaking gas valve (potentially dangerous)

Common Causes

1. Moisture on the flame sensor or PCB
2. Faulty flame sensor (flame rod)
3. Damaged wiring creating electrical interference
4. PCB (circuit board) fault misreading signals
5. Gas valve leak allowing gas through when closed
6. Recent power surge damaging electronics

What You Can Do

DO NOT Reset Repeatedly

⚠️ Important: Do not keep resetting the boiler if E004 returns. This could indicate a gas safety issue.

Safe Actions

1. Turn off the boiler using the control panel
2. Note when the error occurred - during heating, hot water, or after shutdown?
3. Check for recent power outages or electrical issues
4. Ensure good ventilation around the boiler

Call a Gas Safe Engineer

E004 requires professional diagnosis. Do not attempt to fix this yourself.

What the Engineer Will Do

The engineer will systematically check:

1. Flame sensor (rod) - cleaning or replacement
2. Electrical connections - check for moisture or damage
3. Gas valve operation - ensure proper opening/closing
4. PCB condition - test circuits and replace if needed
5. Earthing and bonding - verify electrical safety
6. Flame sensing circuit - check resistance values

Likely Solutions

• Clean or replace the flame sensor
• Dry out moisture from components
• Replace damaged wiring
• Replace the PCB (circuit board)
• Replace the gas valve if leaking
• Improve ventilation to prevent condensation

Prevention

• Annual servicing to keep components clean and dry
• Good ventilation to prevent moisture buildup
• Surge protection on the electrical supply
• Proper installation per manufacturer guidelines

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Applicable Models: NCB-CE, NCB300, NCB500, NCB700, LCB700, and NPE series.

Safety Note: If you smell gas at any time, turn off the gas supply immediately and call the National Gas Emergency Service on 0800 111 999.