Navien Flue Exhaust Thermistor 30009478A

The Navien flue exhaust thermistor is a temperature sensor fitted in the flue exhaust path of Navien NCB and NPE appliances. It reports exhaust gas temperature back to the boiler's control board so the appliance can monitor combustion and flue conditions. It is supplied under part number 30009478A.

• Flue temperature related fault codes or lockouts appearing on the appliance display
• Boiler shutting down or cycling shortly after ignition
• Erratic or implausible flue temperature readings during a service check
• Resistance reading from the thermistor outside the expected range for the ambient temperature
• Intermittent faults that clear on reset but return once the appliance reaches temperature

• Confirm your appliance model against the fitment list above
• Check the serial number of your appliance, as fitment varies across production runs
• Inspect the thermistor wiring and connector for damage before assuming the sensor itself has failed
• Verify the fault with a resistance test at the sensor rather than relying on the fault code alone