High Lockout
F9 on Ideal Logic Combi C24 C30 C35

Your boiler's computer memory is blank or incorrect, meaning it doesn't currently know how to operate itself.

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

PCB Programming - Unprogrammed state

What causes this fault?

This fault occurs when the boiler's main control board loses its identity and can no longer remember which specific model it is installed in. The most common reason is a electronic failure within the PCB itself or a loose Customer ID chip, which acts like a small memory stick that tells the boiler how to function safely.

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

L9View →F2View →L2View →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

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 →