High Lockout
E09 on Potterton Promax HE

Your boiler has detected an electrical connection issue with the gas control system, preventing it from lighting safely.

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

Gas valve wiring fault

What causes this fault?

This fault occurs when the boiler's main control board loses communication with the gas valve, which is the component responsible for releasing fuel into the burner. The most common reason is a loose or damaged electrical connection between these two parts, though it can also be caused by a complete internal failure of the gas valve itself.

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 →

Pilot light keeps going out

Older boilers — thermocouple, draught, gas supply.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →