Flow Thermistor High

Baxi Flow Thermistor Fault Code

Also written as FLOWTHERMISTOR — same fault.

The Baxi Flow Thermistor fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot heat your home or water safely.. It appears on 3 Baxi models 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: Indicator: Upper LED Off, Middle LED On, Lower LED Flash, Bottom LED On. Fault in flow thermistor circuit.
Typical repair cost £90-160 (including labour)

Engineer required

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

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Baxi models that show the Flow Thermistor fault code

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

Source

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

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026