High Lockout
Fault 40 / 102 on Worcester Bosch Greenstar CDi Compact

Your boiler has detected a broken wire or a faulty connection to one of the internal temperature sensors, which is preventing it from heating properly.

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

Temperature sensor T1 on collector group 1 faulty: Break in the sensor lead (T1).

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the main temperature sensor that monitors the heat exchanger. The most common reason is that the sensor has physically failed due to age or heat stress, or the delicate wiring connecting it to the control board 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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