High Lockout
b1 on Worcester Bosch Greenstar Ri

Your boiler's internal computer memory chip is loose or missing, meaning it cannot identify which model it is supposed to be.

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 small memory chip, known as a code plug, becomes loose or fails to communicate with the boiler's main control board. Without this chip, the boiler essentially forgets its own identity and safety settings, leading to an immediate shutdown for security reasons. The most common cause is either physical vibration loosening the connector or an electrical failure within the chip 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 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 →