BoilerFaultCodesViessmann F9 Fault Code
The Viessmann F9 fault code means: your boiler's fan is not spinning fast enough to safely start the burner, causing the system to shut down for safety.. It appears on 18 Viessmann models in our database.
Technical description: Burner in fault state. Fan speed too low at burner start. Cause: Check the fan, check the fan cables and supply, check the fan control. Press E.
What causes the Viessmann F9 fault?
This fault occurs when the boiler's internal computer tries to start the heating process but detects that the fan isn't reaching the necessary speed to clear out exhaust gases. The most common reasons are a build-up of debris causing the fan to stick, a failure in the fan's motor, or a loose electrical connection between the fan and the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Viessmann models that show the F9 fault code
Click a model for the full fault code list and model-specific repair notes.
- Vitodens 050-W Repair: £250-£550
- Vitodens 050-W BPJD 35kW Combi Boiler Repair: £250-450
- Vitodens 100 Compact Repair: £150-300
- Vitodens 100-W B1HA-19
- Vitodens 100-W B1HA-26
- Vitodens 100-W B1HA-30
- Vitodens 100-W B1HA-35
- Vitodens 100-W B1KA-26
- Vitodens 100-W B1KA-30
- Vitodens 100-W B1KA-35
- Vitodens 100-W WB1B Repair: £250-450
- Vitodens 111-W B1LB 26kW Repair: £200-450
- Vitodens 111-W B1LB 35kW Repair: £200-450
- Vitodens 222-F Repair: £250-£550
- Vitodens 242-F B2UA Repair: £250-450
- Vitodens 242-F FB2B Repair: £200-400
- Vitodens 300-W Repair: £250-£550
- Vitodens 333-F Repair: £280-550
Source
Viessmann F9 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 050-W BPJD 35kW Combi Boiler manual (PDF)
- Viessmann Vitodens 100 Compact manual (PDF)
- Viessmann Vitodens 100-W B1KA-35 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026