BoilerFaultCodesViessmann F4 Fault Code
The Viessmann F4 fault code means: your boiler is failing to light the flame needed to heat your water and radiators, which has caused the system to shut down for safety.. It appears on 9 Viessmann models in our database.
Technical description: Burner in fault state. No flame signal is present. Cause: Check the ionisation electrode and leads, measure the ionisation current, check the gas pressure, check the gas combination valve, ignition, ignition module, ignition electrodes and the condensate drain. Press E.
What causes the Viessmann F4 fault?
This fault occurs when the boiler's internal computer tries to start the burner but cannot detect a flame after several attempts. The most common reasons are a dirty or worn-out sensor that can no longer 'see' the flame, or a physical blockage in the gas supply or drainage system preventing ignition. Because the boiler cannot confirm it is burning fuel safely, it shuts down completely to prevent gas from building up.
This fault is more common during freezing winter temperatures, as a blocked or frozen condensate drainage pipe can back up and prevent the boiler from lighting.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the F4 fault code
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Source
Viessmann F4 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026