If an issue occurs with your Viessmann boiler, a fault code may appear on the control panel display.
The Viessmann boiler fault codes, which include letters, numbers, or both, help you and your heating engineer identify and resolve issues either over the phone or in person. Viessmann fault codes apply to all Viessmann boilers, though some are specific to certain models.
If a fault code appears on your Viessmann boiler, refer to the tables below to identify the issue. If you can’t find what you are looking for read our common Viessmann boiler problems guide.
Fault Codes 5C, 5D, 5E, and 5F
Boiler Model
System Behaviour & Diagnosis
Vitotronic 300-K with Vitotronic 200
Control mode – Communication fault – Vitotronic 100 of boiler 5-8
Stand-alone control unit without supply temperature sensor (supply temperature might not be high enough). Short circuit – Common supply temperature sensor
Vitocontrol-S with Vitotronic 100 / Vitotronic 300-K with Vitotronic 200
Vitocontrol-S controls in a stand-alone manner without supply temperature sensor (supply temperature might not be high enough). Common supply temperature sensor shorted out
Vitocrossal 300
Regulates without supply temperature sensor (low-loss header). Short circuit – System flow temperature sensor
Vitodens 200-W / 222-F
Regulates without supply temperature sensor (low-loss header). Short circuit – Supply system temperature sensor
Vitotronic 020/200-H / 200 / 200-H / 300
Mixing valve closes or closed. Short circuit – Supply temperature sensor / mixing valve circuit M1
Vitotronic 300-K with Vitotronic 100
Vitotronic 300-K, MW1S controls in a stand-alone manner without strap-on sensor (supply temperature might not be high enough). Short circuit – Strap-on temperature sensor
Vitodens 200-W
Regulates without supply temperature sensor (low loss header). System supply temperature sensor shorted out
Fault Codes 55, 56, and 57
Boiler Model
System Behaviour & Diagnosis
Vitotronic 300-K with Vitotronic 200
Control mode maintenance or fault on Vitotronic 100 of boiler 5-8
Fault Codes EE and EF
Boiler Model
System Behaviour & Diagnosis
Vitodens 100-W / 200 / 0 / Vitotronic 300
Burner blocked. Faulty air pressure switch – Air damper (flap) stuck
Fault Code FE4
Boiler Model
System Behaviour & Diagnosis
Vitocrossal 200
Burner shuts down. Multiple detection of undervoltage
Fault Codes F-B7, F-F4, F-F2, F-F7, F-F8, and F-F9
Boiler Model
System Behaviour & Diagnosis
Vitocrossal 200
Case A: Burner control unit in a fault state; system cools down; burner control locked out. Case B: Type of coding card. Case A: Coding card not inserted in the burner control unit; faulty or incorrect coding card. Case B: Coding card does not match burner control unit
Fault Codes 50, 51, 58, and 59
Boiler Model
System Behaviour & Diagnosis
Vitodens 200-W / 222-F
No DHW heating / Fault with DHW. Short circuit/open circuit – DHW tank temperature sensor or lead break
Fault Codes A9, BA, BB, BC, and FE0
Boiler Model
System Behaviour & Diagnosis
Vitodens 200
Boiler cools down. Sensor inputs are not read correctly
Fault Codes F-FA, F-FB, and FR
Boiler Model
System Behaviour & Diagnosis
Vitocrossal 200 / 400-620 / 186-311
Fan runs without demand; burner control unit in a fault state. Fan not stopped; cable 100A faulty; fan faulty; burner control unit faulty
Fault Codes 8C, 8D, 8E, and 8F
Boiler Model
System Behaviour & Diagnosis
Vitotronic 300
Burner control unit in a fault state. Lead break, boiler water temperature sensor, burner control unit
Fault Code 52
Boiler Model
System Behaviour & Diagnosis
Vitotronic 300
Control mode. Short circuit – Supply temperature sensor low-loss header
Vitodens 100-W Combiplus
Burner blocked (Combiplus only). Flow sensor shorted out
Fault Code 38
Boiler Model
System Behaviour & Diagnosis
Vitodens 200-W / 222-F / Combiplus
Burner blocked. Boiler water temperature sensor cable broken
Normal operation without influence of return water temperature. Open circuit 1 or 2 – Return water temperature sensor (of mixing valve circuit 1)
Fault Codes A3, B0, F1, E-E1, and F-E2
Boiler Model
System Behaviour & Diagnosis
Vitocrossal 300 / Vitodens 200-W / 222-F / 300
Control mode (stays in factory default setting). Faulty programming unit
Fault Code 28
Boiler Model
System Behaviour & Diagnosis
Vitocontrol-S with Vitotronic 100
Vitocontrol-S, VD2/CT3/CM2 controls in a stand-alone manner w/o supply temperature sensor (supply temperature might not be high enough). Open circuit – Common supply temperature sensor
Vitocontrol-S with Vitotronic 100 / Vitotronic 300-K with Vitotronic 100
Vitocontrol-S, WB2B controls in a stand-alone manner w/o supply temperature sensor (supply temperature might not be high enough). Common supply temperature sensor cable broken
Vitocrossal 300 / Vitodens 200-W / 222-F
Regulates without supply temperature sensor (low-loss header). System supply temperature sensor cable broken
Vitotronic 050/200-H
Mixing valve closes. Cable break – Supply temperature sensor
Vitotronic 050/200-H
Mixing valve is closed. Open circuit – Supply temperature sensor of mixing valve circuit M1
Vitotronic 200-H / Vitotronic 200 / 300
Mixing valve is being closed. Lead break, supply temperature sensor, heating circuit with mixing valve M1 (heating circuit 1)
Vitotronic 300 / 300-K with Vitotronic 300 / 200
Stand-alone control unit without supply temperature sensor (supply temperature might not be high enough). Lead break, common supply temperature sensor
Vitotronic 300-K with Vitotronic 100
Vitotronic 300-K, MW1S controls in a stand-alone manner w/o strap-on sensor (supply temperature might not be high enough). Open circuit – Strap-on temperature sensor
Fault Code B1
Boiler Model
System Behaviour & Diagnosis
Vitocontrol-S with Vitotronic 100 / Vitotronic 100 / 200 / 300 / Vitotronic 300-K with Vitotronic 100
Emissions test mode. Internal electronics fault
Vitocontrol-S with Vitotronic 100 / Vitodens 200-W
Regulates as if the outside temperature is 32°F (0°C). Internal fault
Vitotronic 020/200-H
Undefined control characteristics. Internal electronics fault
Control mode – Lead break, low-loss header supply temperature sensor. Burner blocked / Control mode – Sensor cable broken
CC and F0
Burner in fault mode. Ionisation current too high during calibration – Boiler temperature limiter responded (F2) – Air or blockage in system/pump failure
B6
Control mode. Open circuit – KM bus to solar control unit – Extension AM1 / DE1-DE3 M1 – Communication fault
D5
Burner blocked. Flue gas temperature sensor not properly positioned / Check sensor. External pump fitted on the system (100-W) A-3 fault
60, 68, 70, 78, BD, BE, and BF
No output reduction – Return control open – Boiler with maximum temperature. Short/open circuit – Temperature sensor [17A]
E2 and E3
Burner blocked – Fault: Supply voltage 24V
40 and 44
Mixing valve closes. Heating circuit 2 with mixing valve supply. Short circuit on temperature sensor
48 and 4C
Mixing valve closes or closed. Heating circuit 2 with mixing valve supply temperature sensor cable broken / open circuit
FC
Burner in fault mode. Gas valve faulty or faulty modulation valve control / or vent system blocked. Check the fan, fan cable, and PCB
FE
Burner blocked or in fault mode. Strong interference (EMC) field nearby or faulty main PCB
B2
Control mode – Internal electronics fault
B5
Control mode – External safety equipment
80, 81, 82, 83, and FD
Burner control unit in a fault state; system cools down; burner control unit locked out. Short circuit – Boiler water temperature sensor, burner control unit
B4
Normal operation / Fault around burner control unit. Internal fault (PCB)
C2-C8, CD-CF, D2-D8, DA-DF, and E0
Boiler cools down. Fixed high limit has responded or fuse F2 has blown
F5
Gas pressure switch shows no gas pressure / Electrical connection fault. Gas shut-off valve closed; gas pressure switch faulty; multiple gas problems with gas supply
F6, 58, F9, F-E1, F-E2, and F-F6
Burner in fault mode / Emergency operation. Fan not at standstill / Plug-in connection
How often should I service my Viessmann boiler?
Viessmann recommends annual servicing to ensure optimal performance, safety, and efficiency. Regular gas boiler servicing can prevent common fault codes like A4 or 0C by addressing issues such as air locks or insufficient power supply early.
What does a Viessmann boiler service include?
A standard Viessmann boiler service includes checking the boiler’s components, cleaning key parts, inspecting for leaks or blockages, and testing for fault codes (e.g., D4, EE, or EF). A qualified engineer will also verify gas pressure and system efficiency.
Can I fix Viessmann boiler fault codes myself?
Some fault codes, like 0F (indicating a service is required), can prompt you to schedule professional maintenance. However, most issues, such as those involving burner lockouts (e.g., C1, F-FA) or sensor faults (e.g., 18, D1), require a qualified engineer due to safety risks and technical complexity.
How do I know if I need a new Viessmann boiler?
If your boiler frequently displays fault codes (e.g., F-E1, F-E2, or 38), has high repair costs, or is over 10-15 years old, replacement may be more cost-effective. New Viessmann models, like the Vitodens 100-W, offer improved efficiency and reliability.
How long does it take to install a new Viessmann boiler?
Installation typically takes 4-8 hours for a straightforward replacement, depending on the system complexity and property layout. For more details, see How long does it take to fit a new boiler?.
James Elston has over 15 years experience in the solar panel and central heating industry. His expertise are key in ensure Green Central’s customers receive the best solar panels, batteries and installation service all round. Over the years James has overseen over 20,000 home heating installations and his knowledge in this industry is second to none.
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