Medium Lockout
Fault 51 123 on Worcester Bosch Greenstar CDi Compact

Your boiler has detected that the wrong type of temperature sensor has been installed or configured for your hot water system.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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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

Cylinder temperature sensor type used as collector temperature sensor (T1).

What causes this fault?

This fault occurs when the boiler's control board receives a signal from a temperature sensor that it doesn't recognise or expect. It typically happens because an incompatible part was installed during a repair, or because the internal settings have accidentally been configured for a solar heating system that isn't actually there.

Engineer required

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

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Related fault codes

P1View →

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