Viessmann boiler fault codes
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.
Before you call anyone
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. | Viessmann Vitodens 100-W, Viessmann Vitodens 200-W | Checks first |
| 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 |
Sources
- Viessmann Vitodens 100-W (B1HC/B1KC) installation and service instructions, 5697 787 GB
- Viessmann: how to fix a frozen boiler condensate pipe
Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check