High Lockout
e43 on Remeha Avanta 18V

Your boiler's internal computer settings have become scrambled or have fallen outside of their safe operating ranges, causing the system to shut down for safety.

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

Parameter limits

What causes this fault?

This fault occurs when the boiler's internal memory experiences a software glitch or a physical failure of the electronic circuits. It means the control board can no longer verify its own safety settings, so it shuts down the system to prevent any dangerous operation. The most common cause is a failing Printed Circuit Board (PCB) that has lost its stored configuration data.

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

E36View →E42View →E44View →

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 →