HVACopediaViessmann boiler error codes
158 codes (144 faults, 14 normal display and menu codes).
| Code | Meaning | Severity / type |
|---|---|---|
| A.12 | Real-time clock battery flat | Low |
| A.18 | Possible condensate back-up in heat cell | Medium |
| A.19 | Temperature limiter has responded | Medium |
| A.20 | Service interval could not be activated | Low |
| Connection error | Display link lost to HMU | Menu / mode display |
| F.100 | PlusBus voltage error | Medium |
| F.104 | External fault message input active | Medium |
| F.11 | Solar collector sensor open circuit | Low |
| F.12 | Solar collector sensor short circuit | Low |
| F.13 | Outside temperature sensor open circuit | Low |
| F.14 | Outside temperature sensor short circuit | Low |
| F.142 | CAN bus communication error | High |
| F.143 | Fan overheating (air mass flow sensor / recirculation) | High |
| F.15 | Storage tank sensor open circuit (solar/backup) | Low |
| F.16 | Storage tank sensor short circuit (solar/backup) | Low |
| F.160 | CAN bus communication error (external/internal) | High |
| F.161 | BCU data memory access error | High |
| F.163 | BCU memory checksum error | High |
| F.180 | Gas pressure too low | High |
| F.182 | Outlet temperature sensor short circuit | Medium |
| F.183 | Outlet temperature sensor open circuit | Medium |
| F.184 | Supply temperature sensor / high limit short circuit | High |
| F.185 | Supply temperature sensor / high limit open circuit | High |
| F.29 | Low loss header sensor open circuit | Low |
| F.299 | Time and date incorrect | Low |
| F.30 | Low loss header sensor short circuit | Low |
| F.342 | BCU communication error | High |
| F.345 | Temperature limiter tripped, auto restart after cooling | High |
| F.346 | Ionization current calibration error | High |
| F.348 | Gas modulation valve fault | High |
| F.349 | Air mass flow not detected correctly | High |
| F.350 | Ionization current outside permitted range (BCU) | High |
| F.351 | Ionization current outside permitted range (BCU) | High |
| F.352 | CO limit inside appliance exceeded | Critical |
| F.353 | Insufficient gas supply, output reduced | High |
| F.354 | Gas modulation valve tolerance outside range | High |
| F.355 | Analogue signal reference check: flame signal at start | High |
| F.357 | Insufficient gas supply | High |
| F.359 | No ignition spark | High |
| F.361 | No or weak flame signal at burner start | High |
| F.366 | Gas valve supply does not switch off | Critical |
| F.367 | Gas valve supply does not switch off | Critical |
| F.369 | Flame loss right after ignition (safety time) | High |
| F.370 | Fuel or modulation valve will not close | Critical |
| F.372 | Repeated flame loss during calibration | High |
| F.373 | Heat transfer too low during calibration | High |
| F.377 | Ionization post-adjustment conditions not met | High |
| F.378 | Flame loss during stabilization or operation | High |
| F.379 | Flame signal missing or insufficient | High |
| F.380 | Flame loss right after ignition (safety time) | High |
| F.381 | Flame loss during operation | High |
| F.382 | Error counter limit exceeded | High |
| F.383 | Possible gas line contamination | High |
| F.384 | Possible gas line contamination | High |
| F.385 | Short circuit on ionization signal 1 | High |
| F.386 | BCU faulty | High |
| F.387 | Ionization current ground fault | High |
| F.388 | BCU faulty | High |
| F.395 | IO electrode ground fault | High |
| F.396 | BCU faulty | High |
| F.399 | IO electrode ground fault | High |
| F.400 | BCU faulty | High |
| F.401 | IO electrode ground fault | High |
| F.402 | BCU faulty | High |
| F.403 | IO electrode ground fault | High |
| F.404 | BCU faulty | High |
| F.405 | IO electrode ground fault | High |
| F.406 | BCU faulty | High |
| F.408 | BCU faulty | High |
| F.410 | BCU faulty | High |
| F.416 | Flue gas temperature sensor mispositioned | High |
| F.417 | BCU faulty | High |
| F.418 | BCU faulty | High |
| F.425 | Time synchronization failed | Low |
| F.430 | Gateway communication error | Low |
| F.446 | Supply sensor / high limit deviation | High |
| F.447 | Ionization current signal deviation | High |
| F.448 | Ionization current signal deviation | High |
| F.449 | Program run monitoring error | High |
| F.450 | Program run monitoring error | High |
| F.451 | Program run monitoring error | High |
| F.452 | Program run monitoring error | High |
| F.453 | Sequence synchronization error | High |
| F.454 | Wrong BCU software version | High |
| F.455 | Program run monitoring error | High |
| F.456 | Program run monitoring error | High |
| F.457 | Fan sluggish or blocked | High |
| F.458 | Reset sequence fault | High |
| F.463 | Contaminated combustion air / flue recirculation | High |
| F.464 | Ionization current too low during calibration | High |
| F.467 | Gas supply insufficient during calibration | High |
| F.468 | Ionization current too high during calibration | High |
| F.471 | Sensor circuit fault (call for heat) | Medium |
| F.473 | HMU communication error | High |
| F.474 | Program run monitoring error | High |
| F.477 | Solar differential temperature monitoring | Low |
| F.49 | Flue gas temperature sensor open circuit | High |
| F.5 | Sensor circuit fault at plug 33 (X6) | Low |
| F.50 | Flue gas temperature sensor short circuit | High |
| F.517 | Remote control not working | Low |
| F.527 | Wrong HMU parameter set | High |
| F.528 | Wrong BCU parameter set | High |
| F.530 | Solar sensor missing or open | Low |
| F.538 | System return sensor open (SDIO) | Low |
| F.540 | Condensate back-up in heat cell | High |
| F.544 | HC2 mixed supply sensor open circuit | Medium |
| F.545 | HC2 mixed supply sensor short circuit | Medium |
| F.546 | HC3 mixed supply sensor open circuit | Medium |
| F.547 | HC3 mixed supply sensor short circuit | Medium |
| F.548 | HC4 mixed supply sensor fault (open circuit) | Medium |
| F.549 | HC4 mixed supply sensor short circuit | Medium |
| F.57 | Room temperature sensor open circuit | Low |
| F.574 | HC1 room sensor not available | Low |
| F.58 | Room temperature sensor short circuit | Low |
| F.59 | Supply voltage too low, burner locked out | High |
| F.62 | High limit safety cut-out tripped | Critical |
| F.63 | Flue gas temperature limiter tripped | Critical |
| F.666 | DHW preheating sensor TS3 open circuit | Low |
| F.667 | DHW preheating sensor TS3 short circuit | Low |
| F.668 | DHW reheating sensor TS4 open circuit | Low |
| F.669 | DHW reheating sensor TS4 short circuit | Low |
| F.67 | Ionization current outside permitted range | High |
| F.670 | Buffer sensor TS3 open circuit | Low |
| F.671 | Buffer sensor TS3 short circuit | Low |
| F.672 | Thermostat-function sensor TS3 open circuit | Low |
| F.673 | Thermostat-function sensor TS3 short circuit | Low |
| F.68 | Flame signal present at burner start | High |
| F.69 | Ionization current outside permitted range (valve/electrode check) | High |
| F.691 | No combustion air supply feedback | High |
| F.7 | DHW storage tank sensor open circuit | Medium |
| F.70 | BCU internal error | High |
| F.71 | Fan speed too low | High |
| F.72 | Fan idle state not reached | High |
| F.73 | BCU internal communication error | High |
| F.74 | Water pressure too low, burner locked out | High |
| F.762 | System pressure too low | High |
| F.763 | Gas pressure too high | High |
| F.764 | Lag boiler reports a fault | Medium |
| F.765 | Lead boiler communication error | Medium |
| F.77 | BCU data memory error | High |
| F.8 | DHW storage tank sensor short circuit | Medium |
| F.89 | Internal circulation pump blocked | High |
| F.91 | DIO module communication error | Medium |
| F.92 | ADIO module communication error | Medium |
| F.94 | PlusBus voltage error | Medium |
| I.56 | External demand active | Menu / mode display |
| I.57 | External blocking active | Menu / mode display |
| I.59 | Parameters restored | Menu / mode display |
| P.1 | Service interval reached | Menu / mode display |
| P.4 | Top up heating water | Menu / mode display |
| P.8 | Service due after burner hours | Menu / mode display |
| S.154 | Internal flow switch open | Normal status |
| S.60 | Summer mode active | Normal status |
| S.74 | Heating suppression | Normal status |
| S.75 | DHW recirculation pump active | Normal status |
| S.94 | No demand, external hook-up HC1 | Normal status |
| S.95 | No demand, external hook-up HC2 | Normal status |
| S.96 | No demand, external hook-up HC3 | Normal status |
Models covered
B2HE-120B2HE-150B2HE-199B2HE-85
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.