Viessmann Vitodens boilers show a letter and a number, such as F4. These meanings come from Viessmann's Vitodens 100-W instructions; other Vitodens models can use different codes, so check your manual.
F4 is the Viessmann code people search for most. Viessmann says it's the code you're likely to see on a Vitodens when the condensate pipe has frozen.
| Code | What it means | Models | Can you fix it? |
|---|---|---|---|
| F4 | No flame signal. | Vitodens 100-W (B1HC/B1KC) | Checks first |
| F2 | Burner fault: the temperature limiter has responded. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| F3 | Flame signal already present when the burner starts. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| F8 | Fuel valve closes too late. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| F9 | Fan speed too low when the burner starts. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 0C | Mains voltage too low. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 0A | CO limiter has responded (CO concentration too high), or gas pressure switch has responded (gas pressure too low). | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 5A | Lead break, flow sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 10 | Short circuit, outside temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 18 | Lead break, outside temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 30 | Short circuit, boiler water temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 38 | Lead break, boiler water temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 50 | Short circuit, cylinder temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 51 | Short circuit, outlet temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 52 | Short circuit, flow sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 58 | Lead break, cylinder temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| 59 | Lead break, outlet temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| A3 | Flue gas temperature sensor incorrectly positioned. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| A9 | Communication error, OpenTherm device. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| b0 | Short circuit, flue gas temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| b8 | Lead break, flue gas temperature sensor. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| E3 | Fault in safety chain. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| E5 | Internal fault. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| F0 | Internal fault. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| F1 | Maximum flue gas temperature exceeded. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| FA | Fan idle state not reached. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| FC | Electrical fan control (control unit) faulty. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| Fd | Burner control unit fault. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |
| FF | Burner control unit fault. | Vitodens 100-W (B1HC/B1KC) | No, engineer only |