High Lockout
F10 on Glow-worm Ultracom 2 HXI

Your boiler has detected a problem with the sensor that measures 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

Flow heating thermistor fault

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that monitors the temperature of the water being sent to your radiators. The most common reason is that the sensor has electronically failed or the internal wiring connecting it to the control board has become loose or damaged. Because the boiler no longer knows how hot the water is, it shuts down to prevent the system from overheating.

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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Related fault codes

F1View →F11View →F13View →

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