High Lockout
AC on Worcester Bosch Greenstar 25 HE Combi

Your boiler's internal computer is having trouble communicating with one of its main control parts, meaning the system cannot run.

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

Module not detected.

What causes this fault?

This fault occurs when the boiler's central brain loses its physical connection with one of the primary control modules, preventing it from sending or receiving instructions. The most common reason is an electrical failure within the main circuit board or a loose internal wired connection that has deteriorated over time due to heat and vibration. Because the system can no longer verify that all safety components are connected, it shuts down immediately to prevent damage.

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

B1View →C6View →

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