| Displayed fault code | System characteristics | Cause of fault | Measure |
| 10 | Regulates as if the outside temperature were 0 °C | Short circuit, outside temperature sensor | Check outside temperature sensor |
| 18 | Regulates as if the outside temperature were 0 °C | Lead break, outside temperature sensor | Check outside temperature sensor |
| 19 | Regulates as if the outside temperature were 0 °C | Interruption of RF outside temperature sensor communication (RF outside temperature sensor, KM-BUS to wireless base station, wireless base station or wireless repeater faulty or defective) | Check wireless connection (place RF outside temperature sensor and wireless repeater close to the boiler). Check KM-BUS to wireless base station. Log off outside temperature sensor and wireless repeater, then log them on again. Replace RF outside temperature sensor. Replace wireless repeater. Replace wireless base station |
| 20 | Regulates without flow temperature sensor (low loss header) | Short circuit, system flow temperature sensor | Check the low loss header sensor |
| 28 | Regulates without flow temperature sensor (low loss header) | Lead break, system flow temperature sensor | Check the low loss header sensor. If no low loss header sensor is connected, set code 52:0 |
| 30 | Burner locked out | Short circuit, boiler water temperature sensor | Check boiler water temperature sensors |
| 38 | Burner locked out | Lead break, boiler water temperature sensor | Check boiler water temperature sensors |
| 40 | Mixer is being closed | Short circuit, flow temperature sensor, heating circuit 2 (with mixer) | Check flow temperature sensor |
| 44 | Mixer is being closed | Short circuit, flow temperature sensor, heating circuit 3 (with mixer) | Check flow temperature sensor |
| 48 | Mixer is being closed | Short circuit, flow temperature sensor, heating circuit 2 (with mixer) | Check flow temperature sensor |
| 50 | No DHW heating by the boiler | Short circuit, cylinder temperature sensor | Check cylinder temperature sensor |
| 58 | No DHW heating | No DHW heating by the boiler | Check cylinder temperature sensor |
| 90 | Normal operation | Short circuit, temperature sensor | Check sensor on the solar control module |
| 91 | Normal operation | Short circuit, temperature sensor | Check sensor on the solar control module |
| 92 | No solar DHW heating | Short circuit, collector temperature sensor | Check temperature sensor on the solar control module or the sensor on the Vitosolic |
| 93 | Normal operation | Short circuit, collector return temperature sensor | Check temperature sensor at connection S3 on the Vitosolic |
| 94 | No solar DHW heating | Short circuit, cylinder temperature sensor | Temperature sensor on the solar control module |
| 98 | Normal operation | Lead break, temperature sensor | Check sensor on the solar control module |
| 99 | Normal operation | Lead break, temperature sensor | Check sensor on the solar control module |
| 1A | Burner locked out | Flow sensor 1, left (plug 163) faulty | Replace the sensor |
| 1b | Burner locked out | Flow sensor 2, right (plug 163A) faulty | Replace the sensor |
| 1F | Burner locked out | Differential flow rate too large | Clean heat exchanger by flushing |
| 4C | Mixer is being closed | Lead break, flow temperature sensor, heating circuit 3 (with mixer) | Check flow temperature sensor |
| 9A | No solar DHW heating | Lead break, collector temperature sensor | Check temperature sensor on the solar control module or the sensor on the Vitosolic |
| 9b | Normal operation | Lead break, collector return temperature sensor | Check temperature sensor at connection S3 on the Vitosolic |
| 9C | No solar DHW heating | Lead break, cylinder temperature sensor | Check temperature sensor on the solar control module or the sensor on the Vitosolic |
| 9E | Normal operation | No flow or flow rate too low in the solar circuit, or temperature limiter has responded | Check solar circuit pump and solar circuit. Acknowledge fault message |
| 9F | Normal operation | Solar control module or Vitosolic fault | Replace solar control module or Vitosolic |
| A3 | Burner locked out | Flue gas temperature sensor incorrectly positioned | Fit flue gas temperature sensor correctly |
| A4 | Normal operation | Max. system pressure exceeded | Check system pressure (max. system pressure 6 bar). Check the function and sizing of the diaphragm pressure expansion vessel. Vent the heating system |
| A7 | Normal operation as per delivered condition | Programming unit faulty | Replace the programming unit |
| b0 | Burner locked out | Short circuit, flue gas temperature sensor | Check flue gas temperature sensor |
| b1 | Normal operation as per delivered condition | Communication error, programming unit | Check connections and replace programming unit if necessary |
| b5 | Normal operation as per delivered condition | Internal fault | Replace control unit |
| b7 | Burner locked out | Fault, boiler coding card | Plug in boiler coding card or replace if faulty |
| b8 | Burner locked out | Lead break, flue gas temperature sensor | Check flue gas temperature sensor |
| bA | Mixer regulates to 20 °C flow temperature | Communication error, extension kit for heating circuit 2 (with mixer) | Check extension kit connections and code |
| bb | Mixer regulates to 20 °C flow temperature | Communication error, extension kit for heating circuit 3 (with mixer) | Check extension kit connections and code |
| bC | Normal operation without remote control | Communication error, Vitotrol remote control, heating circuit 1 (without mixer) | Check connections, cable and coding address "A0" in the "Heating circuit" group and the DIP switch on the remote control unit. With wireless remote controls: check transmission path connections; place remote control and wireless repeater close to the boiler. Check KM-BUS connection to wireless base station. Replace the wireless components |
| bd | Normal operation without remote control | Communication error, Vitotrol remote control, heating circuit 2 (with mixer) | Check connections, cable and coding address "A0" in the "Heating circuit" group and the remote control settings. With wireless remote controls: check transmission path connections; place remote control and wireless repeater close to the boiler. Check KM-BUS connection to wireless base station. Replace the wireless components |
| bE | Normal operation without remote control | Communication error, Vitotrol remote control, heating circuit 3 (with mixer) | Check connections, cable and coding address "A0" in the "Heating circuit" group and the remote control settings. With wireless remote controls: check transmission path connections; place remote control and wireless repeater close to the boiler. Check KM-BUS connection to wireless base station. Replace the wireless components |
| bF | Normal operation | Wrong LON communication module | Replace LON communication module |
| C1 | Normal operation | Communication error, EA1 extension | Check the connections |
| C2 | Normal operation | Communication error, solar control module or Vitosolic | Check solar control module or Vitosolic |
| C3 | Normal operation | Communication error, AM1 extension | Check the connections |
| C4 | Normal operation | Communication error, OpenTherm extension | Check OpenTherm extension |
| C5 | Normal operation, max. pump speed | Communication error, variable speed pump | Check pump KM-BUS |
| Cd | Normal operation | Communication error, Vitocom 100 (KM-BUS) | Check connections, Vitocom 100 and coding address "95" in group "General"/1 |
| CF | Normal operation | Communication error, LON communication module | Replace LON communication module |
| d6 | Normal operation | DE1 input at EA1 extension reports a fault | Remedy fault at affected appliance |
| d7 | Normal operation | DE2 input at EA1 extension reports a fault | Remedy fault at affected appliance |
| d8 | Normal operation | DE3 input at EA1 extension reports a fault | Remedy fault at affected appliance |
| dA | Normal operation without room influence | Short circuit, room temperature sensor, heating circuit 1 (without mixer) | Check room temperature sensor, heating circuit 1 |
| db | Normal operation without room influence | Short circuit, room temperature sensor, heating circuit 2 (with mixer) | Check room temperature sensor, heating circuit 2 |
| dC | Normal operation without room influence | Short circuit, room temperature sensor, heating circuit 3 (with mixer) | Check room temperature sensor, heating circuit 3 |
| dd | Normal operation without room influence | Lead break, room temperature sensor, heating circuit 1 (without mixer) | Check room temperature sensor, heating circuit 1 and the remote control settings |
| dE | Normal operation without room influence | Lead break, room temperature sensor, heating circuit 2 (with mixer) | Check room temperature sensor, heating circuit 2 and the remote control settings |
| dF | Normal operation without room influence | Lead break, room temperature sensor, heating circuit 3 (with mixer) | Check room temperature sensor, heating circuit 3 and the remote control settings |
| E0 | Normal operation | External LON subscriber fault | Check connections and LON subscribers |
| E3 | Burner in a fault state | Heat transfer too low during calibration. Temperature limiter has shut down | Ensure adequate heat transfer. Press reset button R |
| E4 | Burner locked out | Fault, 24 V supply voltage | Replace control unit |
| E5 | Burner locked out | Flame amplifier fault | Replace control unit |
| Eb | Burner in a fault state | Repeated flame loss during calibration | Check gap between ionisation electrode and burner gauze assembly. Check the allocation of the gas type. Check flue system; remove flue gas recirculation if necessary. Press reset button R |
| EC | Burner in a fault state | Parameter fault during calibration | Press reset button R or replace the boiler coding card and then press reset button R |
| Ed | Burner in a fault state | Internal fault | Replace control unit |
| F0 | Burner locked out | Internal fault | Replace control unit |
| F1 | Burner in a fault state | Flue gas temperature has exceeded limit | Check heating system fill level. Vent the system. Press reset button R after the flue system has cooled down |
| F2 | Burner in a fault state | Boiler water temperature sensor has responded | Check heating system fill level. Check circulation pump. Vent the system. Check boiler water temperature sensor and connecting cables. Press reset button R |
| F6 | Burner in a fault state | Temperature values of the boiler water temperature sensors vary too widely from one another | Replace the boiler water temperature sensors |
| F8 | Burner in a fault state | Fuel valve closes late | Check gas solenoid valve. Check both control paths. Press reset button R |
| FF | Burner blocked or in a fault state | Internal fault or reset button R blocked | Restart the appliance. Replace the control unit if the appliance will not restart |