High Lockout
9P on Ideal Maximiser SE

Your boiler's computer brain has suffered a serious internal electronic failure and can no longer communicate with the heating system.

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

Internal failure control panel or defective ModuLine.

What causes this fault?

This fault occurs when the boiler's internal computer experiences a critical electronic crash or a hardware failure within its circuitry. It is usually caused by the degradation of sensitive electrical components over time or a sudden power surge that damages the communication links on the control board. When this happens, the brain of the boiler can no longer send instructions to the burner or pump, leading to a total system shutdown.

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 →