High Lockout
F11 on Glow-worm Ultracom hxi

Your boiler has detected an issue with the sensor that monitors the temperature of the water coming back from your radiators, preventing it from heating your home safely.

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

Return heating thermistor fault

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor has developed an internal electrical failure 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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Related fault codes

F10View →F12View →F13View →

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