High Lockout
FAIL POINT I on Worcester Bosch Greenstar Si

Your boiler has detected an electrical issue with one of its internal sensors or the gas valve, causing the system to shut down for safety.

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

Sensor Fault (ST16 connector, DHW sensor, CH sensor, or gas valve electrical readings).

What causes this fault?

This fault occurs when the boiler's main control board receives an incorrect or missing electrical signal from one of its vital components. It is usually triggered by a faulty temperature sensor that can no longer measure water heat accurately, or a failing electrical connection to the gas valve which prevents the system from firing 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.

Find a Gas Safe engineer
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