High Lockout
b1 on Worcester Bosch Greenstar CDi Compact

Your boiler’s internal computer has lost contact with a small identification chip that tells it how to operate correctly.

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

Code plug not detected

What causes this fault?

This fault occurs when the boiler's main control board can no longer read the small identification chip, known as a code plug, which contains the unit's specific settings. The most common reasons are a loose connection caused by natural vibrations over time or a physical 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.

Find a Gas Safe engineer
Search the official register →

Related fault codes

9AView →208View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →