Flue Thermistor Fault High

Keston Flue Thermistor Fault Fault Code

Also written as FLUETHERMISTORFAULT — same fault.

The Keston Flue Thermistor Fault fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the exhaust fumes leaving the unit, causing it to stop operating for safety reasons.. It appears on 1 Keston model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Check Flue Thermistor Wiring, Check Flue Thermistor
Typical repair cost £150-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Keston models that show the Flue Thermistor Fault fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Keston Flue Thermistor Fault fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026