Viessmann is a German heating technology company founded in 1917. Known for producing premium, highly efficient boilers, their Vitodens range is popular in the UK for its exceptional reliability and advanced controls. Viessmann uses alphanumeric fault codes which vary by model and controller type.
Viessmann Boiler Fault Codes
All Viessmann Fault Codes 70
| Code | Fault | Severity | Type | View guide |
|---|---|---|---|---|
| 02 | DHW Sensor Short Circuit The domestic hot water NTC sensor wiring has a short circuit. | Medium | Engineer | View Guide |
| 04 | Flow Sensor Short Circuit The flow NTC wiring has a short circuit. | Medium | Engineer | View Guide |
| 05 | Return Sensor Short Circuit The return NTC wiring has a short circuit. | Medium | Engineer | View Guide |
| 06 | Flow Sensor Open Circuit The flow NTC circuit is broken. | Medium | Engineer | View Guide |
| 07 | Return Sensor Open Circuit The return NTC circuit is broken. | Medium | Engineer | View Guide |
| 08 | DHW Sensor Open Circuit The DHW NTC circuit is broken. | Medium | Engineer | View Guide |
| 09 | Combustion Chamber Sensor Fault The combustion chamber NTC has a fault. | High | Engineer | View Guide |
| 0A | Flow Temperature Sensor Fault The flow NTC is reading outside expected range. | Medium | Engineer | View Guide |
| 0B | Fan Speed Error — Wind Conditions On Vitodens 200 boilers, code 0B indicates the fan has not idled correctly after an… | Medium | Engineer | View Guide |
| 0C | Flame After Shutdown (Vitodens 200) On Vitodens 200-W boilers, code 0C indicates a flame signal was still present after the… | High | Engineer | View Guide |
| 0D | Gas Valve Fault The gas valve is not responding to commands. | High | Engineer | View Guide |
| 0E | PCB Fault Internal error on the printed circuit board. | High | Engineer | View Guide |
| 0F | Boiler Service Required Not a fault — this is a maintenance reminder indicating the boiler is due for… | Low | DIY Check | View Guide |
| 10 | DHW Outlet Temperature Sensor Short Circuit The domestic hot water outlet temperature sensor has a short circuit. The boiler cannot accurately… | Medium | Engineer | View Guide |
| 11 | Fan Speed Too Low The fan is running below minimum speed. | High | Engineer | View Guide |
| 12 | Fan Speed Too High The fan is running faster than expected. | Medium | Engineer | View Guide |
| 14 | Pump Blocked The pump is blocked or seized. | High | Engineer | View Guide |
| 15 | Pump Running Dry The pump is running but no water is being circulated. | High | Engineer | View Guide |
| 16 | Flame Instability The flame signal is fluctuating. | High | Engineer | View Guide |
| 18 | Pump Blocked or Not Running The circulation pump is not responding or is mechanically blocked. Water cannot flow through the… | High | Engineer | View Guide |
| 19 | Ignition Lead Fault The ignition lead or electrode is faulty. | High | Engineer | View Guide |
| 20 | Diverter Valve Fault The diverter valve is stuck. | Medium | Engineer | View Guide |
| 22 | Three-Way Valve Stuck The diverter valve is stuck in one position. | Medium | Engineer | View Guide |
| 24 | Rapid Temperature Rise Flow temp rising too fast. | High | Engineer | View Guide |
| 25 | Flow/Return Differential Temperature gap too large. | Medium | Engineer | View Guide |
| 30 | Boiler Water Temperature Sensor Short Circuit The main boiler water temperature sensor (NTC) has short-circuited. On some Viessmann models the burner… | Medium | Engineer | View Guide |
| 32 | Low Gas Pressure Gas pressure insufficient. | High | Engineer | View Guide |
| 34 | Mains Voltage Fault Voltage outside range. | Medium | Engineer | View Guide |
| 36 | Phase/Neutral Reversed Polarity reversed. | High | Engineer | View Guide |
| 38 | Boiler Water Temperature Sensor Open Circuit The main boiler water temperature sensor cable has broken or become disconnected. | Medium | Engineer | View Guide |
| 40 | Internal Bus Communication Fault There is a communication fault on the internal data bus between boiler components. The PCB… | High | Engineer | View Guide |
| 42 | Coding Error Boiler configuration incorrect. | High | Engineer | View Guide |
| 44 | Flue Sensor Short Circuit The flue gas NTC has a short circuit. | Medium | Engineer | View Guide |
| 45 | Flue Sensor Open Circuit The flue gas NTC circuit is broken. | Medium | Engineer | View Guide |
| 48 | eBUS Communication Fault The eBUS line between boiler and controller has failed. | Medium | Engineer | View Guide |
| 50 | No Flame Detected The boiler has attempted ignition but no flame has been detected by the ionisation electrode. | High | Engineer | View Guide |
| 51 | Flame Signal Present Without Gas Release The ionisation electrode is detecting a flame even though the gas valve should be closed.… | High | Engineer | View Guide |
| 54 | Condensate Blocked The condensate drain is blocked or frozen. | Medium | DIY Check | View Guide |
| 56 | EEPROM Error PCB memory error. | High | Engineer | View Guide |
| 58 | Combustion Quality Combustion outside limits. | High | Engineer | View Guide |
| 5C | Outdoor Temperature Sensor Open Circuit The outdoor temperature sensor wiring has an open circuit or is disconnected. | Low | Engineer | View Guide |
| 60 | Fan Speed Fault The fan is running outside its expected speed range. | High | Engineer | View Guide |
| 62 | Pump Kickback Fault Pump restart failed. | Medium | Engineer | View Guide |
| 68 | Frost Protection Active Frost protection running. | Medium | DIY Check | View Guide |
| 70 | Outdoor Sensor Open Circuit The outdoor NTC sensor circuit is broken. | Low | Engineer | View Guide |
| 71 | Outdoor Sensor Short Circuit The outdoor sensor wiring has a short circuit. | Low | Engineer | View Guide |
| 73 | Water Pressure Sensor Fault The electronic pressure sensor is reading incorrectly. | Medium | Engineer | View Guide |
| 77 | Frost Protection Active The boiler is running frost protection cycles. | Medium | DIY Check | View Guide |
| 90 | Coding Plug Fault The boiler's coding plug cannot be read. | High | Engineer | View Guide |
| 91 | Appliance Variant Error The boiler variant is not correctly configured. | High | Engineer | View Guide |
| 92 | Air/Gas Mixture Setting Error The combustion air/gas ratio is not within the acceptable range. The boiler is not burning… | High | Engineer | View Guide |
| 95 | Flame Detected After Shutdown Flame signal present when gas valve should be closed. | High | Engineer | View Guide |
| A3 | Flue Gas Temperature Limiter The flue gas temperature has exceeded the safety limit. The boiler has shut down to… | High | Engineer | View Guide |
| A4 | Air Lock in Pump / Insufficient Flow (Vitodens 222-F) On Vitodens 222-F boilers, code A4 indicates an air lock in the internal circulation pump… | Medium | DIY Check | View Guide |
| A6 | Low Gas Pressure The boiler is detecting insufficient gas pressure to operate safely. The gas supply may be… | High | Engineer | View Guide |
| A9 | Condensate Drain Blocked The condensate drain is blocked or cannot flow freely. The boiler has detected that condensate… | Medium | DIY Check | View Guide |
| B1 | Coding Plug Missing The boiler's coding plug is missing or not read correctly. The boiler cannot verify its… | High | Engineer | View Guide |
| C1 | Differential Air Pressure Sensor Open Circuit The differential air pressure sensor has an open circuit, indicating a fault with the sensor… | High | Engineer | View Guide |
| CE | Water Pressure Too Low (GB162) On Worcester Bosch GB162 and Viessmann commercial boilers, CE (code 207) indicates the system water… | Low | DIY Check | View Guide |
| E0 | Safety Temperature Limiter Triggered The boiler has exceeded its maximum safe water temperature. The safety limiter has shut down… | High | Engineer | View Guide |
| E1 | Outdoor Temperature Sensor Fault The outdoor temperature sensor is not reading correctly. Weather-compensated heating control will not function. | Low | Engineer | View Guide |
| E4 | Burner Start Flame Signal Too Weak The burner attempted to start but the ionisation signal (flame detection) was too weak or… | Medium | DIY Check | View Guide |
| EA | Ignition Failure / No Flame Detected On Viessmann Vitodens boilers, code EA (or E4 on some models) indicates the burner flame… | Medium | DIY Check | View Guide |
| F2 | Burner Start Fault The burner has failed to ignite after the start-up sequence. The gas supply, ignition electrode,… | High | Engineer | View Guide |
| F3 | Flame Signal Lost During Operation The flame was detected but has been lost during normal operation. This may be caused… | High | Engineer | View Guide |
| F4 EE | Frozen Condensate Pipe Viessmann's specific code for a frozen or blocked condensate pipe. The most common Vitodens winter… | Medium | DIY Check | View Guide |
| F5 | Gas Pressure Switch / No Gas Pressure The gas pressure switch is showing no gas pressure, or there is an electrical connection… | High | Engineer | View Guide |
| F6 | Low Water Pressure The system water pressure has dropped below the minimum safe level. The boiler cannot circulate… | Low | DIY Check | View Guide |
| FC | Gas Valve Fault / Flue Blocked On Viessmann boilers, code FC indicates either a gas valve fault, a faulty modulation valve… | High | Engineer | View Guide |
| FE | EMC Interference / PCB Fault Strong electromagnetic interference (EMC) nearby or a faulty main PCB is causing the burner to… | High | Engineer | View Guide |