High Lockout
8.b on Worcester Bosch Greenstar CDi Compact

Your boiler's internal configuration chip has been disconnected or is not being recognised correctly by the control board.

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 number

What causes this fault?

This fault occurs when the boiler's control board loses communication with a small memory chip called a code plug, which tells the boiler how to operate. The most common reason is a loose connection caused by general vibration over time or a hardware failure within the chip or the main 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

208View →212View →C1View →

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 →