High Lockout
F7 on Worcester Bosch CDi Classic

Your boiler thinks it sees a flame even though it should be turned off, which prevents it from starting up safely.

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

Flame detected even though the appliance is switched off – check the electrode assembly is dry and the pcb and flue are clear.

What causes this fault?

This fault occurs when the boiler's control system detects an electrical current that signals a flame is present, even though the gas should be turned off. This is often caused by moisture on the internal sensors or a failing circuit board that is misinterpreting signals. Essentially, the boiler enters a safety mode because it cannot guarantee it is safe to ignite the gas.

This issue can occasionally follow heavy wind or rain, as moisture driven into the flue can dampen the internal electrodes and trigger a false reading.

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.

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