High Lockout
EF on Ideal Maximiser SE

Your boiler's main internal computer has developed a fault and can no longer control the heating system 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

Defective control panel.

What causes this fault?

This fault occurs when the boiler's internal computer chips or electrical circuits suffer a hardware failure, meaning it can no longer send or receive instructions to other parts like the pump or gas valve. The most common reason is general wear and tear of the electronic components, or sometimes a power surge that damages the sensitive circuitry on the board.

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 →