High Lockout
Fault 40 / 101 on Worcester Bosch Greenstar CDi Compact

Your boiler has detected an electrical fault with one of its internal temperature sensors, which is preventing it from monitoring heat levels safely and will likely stop it from working.

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: Short circuit on the sensor lead (T1).

What causes this fault?

This fault occurs when the boiler's main control board loses its ability to accurately measure the water temperature because the sensor's electrical circuit has been broken or crossed. The most common reason is that the internal sensor has failed due to age, or the wiring connecting it has become damaged or loose, preventing the boiler from operating safely.

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

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