BoilerFaultCodesIdeal Flow Thermistor Fault Fault Code
Also written as FLOWTHERMISTORFAULT — same fault.
The Ideal Flow Thermistor Fault fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, causing it to shut down as a safety precaution.. It appears on 8 Ideal models in our database.
Technical description: Wiring or resistance issues with the Flow Thermistor located in the flow pipe (upper RHS of boiler).
What causes the Ideal Flow Thermistor Fault fault?
This fault occurs when the internal sensor responsible for measuring the heat of the water leaving your boiler fails or sends an incorrect signal to the control board. The most common reason is that the sensor's internal electrical resistance has drifted out of range due to age, or the wiring connecting it to the main computer has become loose or damaged.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Ideal models that show the Flow Thermistor Fault fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal Flow Thermistor Fault fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026