BoilerFaultCodesWhat the manual says
Manufacturer manualBurner in fault state. The flame signal is already present at burner start. Cause: Check the ionisation electrode and leads. Press E.
What causes this fault?
This fault occurs when the boiler's internal computer detects a flame signal at a time when there shouldn't be one, such as during the initial safety check before ignition. The most common cause is a faulty or soot-covered ionisation electrode that is sending a false electrical signal, or moisture trapped within the burner's wiring. Because the boiler cannot verify that the burner is truly off, it shuts down as a safety precaution to prevent a buildup of unburnt gas.
This fault can be more frequent during periods of high humidity or heavy rain, as moisture entering the air intake can interfere with the sensitivity of the ionisation probes.
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.
Avoid the next call-out bill
A cover plan would handle faults like F3: no call-out fees, no surprise bills.
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Related fault codes
All 75 fault codes on the Vitodens 333-F
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