High Lockout
B1 on Worcester Bosch ZWB 7-25

Your boiler is struggling because a small internal identification chip that tells the system how to operate correctly has come loose or is not being recognised.

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

Coding plug not detected.

What causes this fault?

This fault occurs when the boiler's main control board loses communication with a small memory chip called a code plug, which contains the boiler's essential operating software. The most common reason is a loose connection between the two components, though it can also be caused by a complete electronic failure of the chip or the circuit board itself.

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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