Vaillant ecoTEC boilers show faults as F. followed by a number. Find your code below to see what it means, what you can safely check, and when you need a Gas Safe engineer.
Most winter callouts for Vaillant boilers are F.22 (low pressure) and F.28 (failed to light). Both often have a simple cause you can check yourself: the pressure gauge, your gas supply, and whether the condensate pipe outside has frozen.
| Code | What it means | Models | Can you fix it? |
|---|---|---|---|
| F.22 | Low water pressure in the system. | ecoTEC plus | Usually yes |
| F.28 | No flame detected when the boiler tried to light. | ecoTEC plus | Checks first |
| F.75 | No pressure rise detected when the pump started. | ecoTEC plus | Checks first |
| F.29 | The flame went out during use and the boiler could not relight. | ecoTEC plus | Checks first |
| F.83 | No temperature change detected when the burner started. | ecoTEC plus | Checks first |
| F.23 | The temperature difference between flow and return is too great. | ecoTEC plus | No, engineer only |
| F.72 | Flow or return temperature sensor fault. | ecoTEC plus | No, engineer only |
| F.20 | The safety cut-out has stopped the gas because the boiler overheated. | Vaillant boilers (Vaillant's fault code list) | No, engineer only |
| F.25 | The flue gas temperature is too high. | ecoTEC plus | No, engineer only |
| F.27 | A flame signal was detected while the burner should be off. | ecoTEC plus | No, engineer only |
| F.61 | A fault in the gas valve control. | ecoTEC plus | No, engineer only |
| F.62 | The flame went out later than expected after switch-off. | ecoTEC plus | No, engineer only |
| con | No communication with the PCB. | ecoTEC plus | No, engineer only |
| F.00 | Flow temperature sensor interruption. | ecoTEC plus | No, engineer only |
| F.01 | Return temperature sensor interruption. | ecoTEC plus | No, engineer only |
| F.10 | Flow temperature sensor short circuit. | ecoTEC plus | No, engineer only |
| F.11 | Return temperature sensor short circuit. | ecoTEC plus | No, engineer only |
| F.13 | Warm start sensor or cylinder sensor short circuit. | ecoTEC plus | No, engineer only |
| F.24 | Safety switch-off: temperature rise too fast. | ecoTEC plus | No, engineer only |
| F.32 | Fan fault. | ecoTEC plus | No, engineer only |
| F.49 | eBUS fault. | ecoTEC plus | No, engineer only |
| F.63 | EEPROM fault. | ecoTEC plus | No, engineer only |
| F.64 | Electronics or temperature sensor fault. | ecoTEC plus | No, engineer only |
| F.65 | Electronics temperature fault. | ecoTEC plus | No, engineer only |
| F.67 | Electronics or flame fault. | ecoTEC plus | No, engineer only |
| F.68 | Unstable flame signal. | ecoTEC plus | No, engineer only |
| F.70 | Invalid device specific number (DSN). | ecoTEC plus | No, engineer only |
| F.71 | Flow temperature sensor fault. | ecoTEC plus | No, engineer only |
| F.73 | Water pressure sensor signal in the wrong range (too low). | ecoTEC plus | No, engineer only |
| F.74 | Water pressure sensor signal outside the correct range (too high). | ecoTEC plus | No, engineer only |
| F.76 | Overheating protection on the primary heat exchanger has responded. | ecoTEC plus | No, engineer only |
| F.77 | Flue non-return flap or condensate pump fault. | ecoTEC plus | No, engineer only |
| F.85 | Flow and return temperature sensors incorrectly installed. | ecoTEC plus | No, engineer only |
| F.87 | Ignition transformer not connected. | ecoTEC plus | No, engineer only |
| F.88 | Gas valve not connected. | ecoTEC plus | No, engineer only |
| F.89 | Incorrect pump detected. | ecoTEC plus | No, engineer only |