High Lockout
E80-450 on Worcester Bosch 24/28CDi II RSF

Your boiler has detected a failure with the internal gas control valve, meaning it cannot safely ignite to provide heating or hot water.

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 – Natural Gas Dungs BM771 SL 040

What causes this fault?

This fault occurs when the boiler's main control board loses electrical communication with the gas valve or detects that the valve is physically unable to open. The most common reason is an internal mechanical failure within the valve itself or a loose connection in the wiring harness that prevents the flow of gas required for ignition.

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

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Pilot light keeps going out

Older boilers — thermocouple, draught, gas supply.

Read →