High Lockout
F08 on Glow-worm Ci Plus

Your boiler has detected a sensor error that prevents it from accurately measuring the temperature of the water returning from your radiators.

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

Central heating return NTC fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the water coming back from your radiators fails or provides an illogical reading. The most common reason is that the sensor's internal electrical resistance has drifted out of range, but it can also be caused by loose or corroded wiring connections following years of vibration and heat cycles.

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

F01View →F06View →

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