Medium Lockout
F12 on Ferroli BlueHelix Pro 25C

Your boiler's hot water sensor has stopped working, meaning the system cannot accurately monitor the temperature of the water coming out of your taps.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

DHW sensor error

What causes this fault?

This fault occurs when the boiler's internal sensor for hot water has failed or is producing an erratic electrical signal. The most common reason is that the sensor's internal thermistor has degraded over time or the wiring connecting it to the main control board has become loose or corroded.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F10View →F11View →F14View →

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