Emergency Lockout
FA306 on Worcester Bosch CDi Classic

Your boiler is still detecting a flame even though the gas supply should have been cut off, which is a safety concern that prevents the unit from operating.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description

Ionisation detected after the gas valve closed

What causes this fault?

This fault occurs when the boiler's internal sensors continue to detect a flame or electrical current after the heating cycle has finished and the gas should be turned off. The most common reason is a gas valve that is stuck open or leaking, though it can also be caused by a sensor that is damaged and sending a false signal to the control board.

Engineer required

This is a emergency 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

C6View →F7View →

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 →