High Lockout
Flow Thermistor Fault on Ideal Logic Max Heat

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Wiring or resistance issues with the Flow Thermistor located in the flow pipe (upper RHS of boiler).

What causes this 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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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