Navien Error Code E016

What Does E016 Mean?

Error code E016 is a heat exchanger overheat fault - a critical safety shutdown that occurs when the heat exchanger temperature exceeds safe limits.

⚠️ This is a serious fault that requires immediate attention from a qualified engineer.

Why Overheating Occurs

Circulation Problems

1. Pump failure - not circulating water through the system
2. Seized pump - pump runs but impeller doesn't turn
3. Airlock in the pump preventing water flow
4. Closed or blocked valves restricting circulation

System Issues

1. Heavy scale buildup on the heat exchanger
2. Blocked pipework restricting flow
3. Insufficient water volume in the system
4. Faulty bypass valve not allowing flow

Component Faults

1. Faulty overheat thermostat giving false readings
2. PCB fault not controlling the burner properly
3. Gas valve stuck open allowing continuous firing
4. Faulty temperature sensors misreading temperatures

Immediate Actions

Safety First

1. Turn off the boiler immediately
2. Do not attempt to restart - this is a safety lockout
3. Allow the boiler to cool completely (at least 30 minutes)
4. Call a Gas Safe engineer - do not attempt DIY repairs

What NOT To Do

• ❌ Don't keep resetting the boiler
• ❌ Don't ignore the error
• ❌ Don't attempt to override safety features
• ❌ Don't operate the boiler if it smells hot or shows scorch marks

⚠️ If you smell gas at any point, turn off the gas at the meter and call the National Gas Emergency line on 0800 111 999.

Why This Is Serious

Overheating can cause:

• Heat exchanger damage requiring expensive replacement
• Boiler fire risk if unchecked
• System contamination from damaged components
• Pressure relief valve activation causing leaks
• Seal and gasket failure throughout the system

What the Engineer Will Do

Diagnostic Checks

1. Verify the overheat has occurred (not a sensor fault)
2. Check pump operation - electrically and mechanically
3. Test system circulation and flow rates
4. Measure water temperature throughout the system
5. Inspect heat exchanger for scale and damage

Likely Repairs

• Replace failed pump
• Flush the system to remove scale and sludge
• Replace overheat thermostat if faulty
• Repair or replace PCB
• Service or replace gas valve
• Clean or replace heat exchanger
• Add system inhibitor to prevent corrosion

Prevention

Regular Maintenance

• Annual boiler service to check all safety devices
• System flush every 5-6 years to prevent scale
• Pump check during each service
• Inhibitor levels maintained in the system

System Design

• Adequate flow rates through the boiler
• Properly sized pipework throughout
• Correct pump specification for the system
• Bypass valve correctly set

Water Quality

• Inhibitor treatment to prevent scale and corrosion
• Magnetic filter to capture debris
• Water quality checks during servicing

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

Critical Note: E016 is not a fault you can ignore. Continued overheating can cause catastrophic boiler failure and potential fire risk. Always call a qualified engineer immediately when this error appears.