High Lockout
E85740 on Potterton Powermax HE

Your boiler has detected an issue with the sensor that confirms the flame is safely lit, 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

Ionization Probe & lead c/w Gasket & 2 screws

What causes this fault?

This fault occurs when the boiler's control system cannot detect a steady flame, causing it to shut down for safety. The most common reason is a buildup of carbon or debris on the ionization probe, which prevents it from sending a signal, or a failure in the electrical lead connecting the probe to the main 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 fault codes

E02View →E04View →

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 →