Viessmann Vitodens 100 (WB1A) fault codes
Built 2004–2007
The first-generation wall-hung Vitodens 100 and the 100-W WB1A that replaced it share a control unit with its own table: an air pressure switch (F5), a water pressure sensor (F7), low water pressure as a code (E6) and a low-flow code (0b), none of which survive into the WB1B.
Codes on the Vitodens 100 (WB1A) follow the same Viessmann scheme as the rest of the range. Where a code behaves differently on this generation, the code page says so.
Viessmann fault codes
Every published Viessmann code. Open a code to see which models and years it applies to.
- F4No flame signal was detected during burner start on any two-character Vitodens, so the burner has locked out. Reset once; if it returns, call a Gas Safe engineer.Stop — call an engineer
- F.74System pressure too low on a 2020-on Vitodens with the numeric display. The burner and pump stop until the pressure is back. Viessmann tell the householder to top up below 1.0 bar.Get it checked
- F.65No flame signal at burner start on a 2020-on Vitodens — the numeric table's equivalent of F4. Burner locked out. Check the gas is on, reset once; if it returns, call a Gas Safe engineer.Stop — call an engineer
- EAA Lambda Pro combustion-controller code on Vitotronic-controlled 200-W, 222-F and 242-F boilers: the ionisation current during calibration was outside the permissible range or implausibly different from last time. Lockout; engineer.Stop — call an engineer
- F2The temperature limiter has responded — the boiler water got hot enough to trip the safety chain. Viessmann want the fill level, pump and limiter checked before any reset.Stop — call an engineer
- F.62The high limit safety cut-out has tripped on a 2020-on Vitodens: the boiler water got too hot and the burner is locked out. A Gas Safe engineer checks circulation, fill level and diverter valve.Stop — call an engineer
- F3The control unit saw a flame signal before it had opened the gas — a flame where there should be none, or a false signal from the ionisation electrode. Lockout; Gas Safe engineer.Stop — call an engineer
- A9On a 100-W, 111-W or 050-W, A9 is a communication error with the OpenTherm room controller: the boiler carries on heating without it. On a 242-F it means the internal pump is blocked.Usually simple to fix
- E3A fault in the safety chain — the temperature limiter circuit has opened or its wiring has failed. Not a sensor fault; a Gas Safe engineer checks the limiter and control unit.Stop — call an engineer
- F.87System pressure too high on a numeric-display Vitodens. Burner and internal pump stop. Usually an overfilled system or a flat expansion vessel; the contractor checks vessel charge and the pressure sensor.Get it checked
- F1Maximum flue gas temperature exceeded. The flue gas sensor has seen the heat exchanger run too hot, almost always because water is not moving through it. Lockout; engineer.Stop — call an engineer
- F9Fan speed too low during burner start. The control unit will not release gas until the fan proves it is turning fast enough, so the burner has locked out. Engineer job.Get it checked
- 30Boiler water temperature sensor fault: 30 is a short circuit, 38 a lead break. The burner is blocked until the sensor reads plausibly again. Engineer replaces the sensor.Get it checked
- E5Viessmann call E5 an "internal fault" but their only instruction is to check the ionisation electrode and its cables — a flame-monitoring fault, blocked not locked, and one for a Gas Safe engineer.Get it checked
- F.71Fan fault on a 2020-on Vitodens: F.71 and F.371 speed too low, F.72 fan still turning, F.457 sluggish or blocked, F.349 air flow not detected. Burner locked out; an engineer checks the fan unit.Get it checked
- F.75No flow rate detected through a 2020-on Vitodens. Viessmann start with top up and vent; if it recurs the engineer checks the boiler isolating valves, flow sensor and pump.Get it checked
- F.352The combustion controller measured carbon monoxide above its limit on a 2020-on Vitodens and locked the burner out. Leave it off. The whole flue gas path is inspected by a Gas Safe engineer.Stop — call an engineer
- F.357Insufficient gas supply on a 2020-on Vitodens. F.353 is the softer version with output reduced; F.467, F.383 and F.384 blame calibration or a contaminated gas line. Check the gas is on, then call an engineer.Get it checked
- F.359No ignition spark on a 2020-on Vitodens, so the burner locked out before it could light. Ignition electrode, ignition module or heat management unit: a Gas Safe engineer's diagnosis.Stop — call an engineer
- F.381Flame lost while the burner was running on a 2020-on Vitodens and it has locked out; F.378 is the same event. The gas supply, flue and ionisation electrode are for a Gas Safe engineer.Stop — call an engineer
- F.540Condensate has backed up into the heat cell of a 2020-on Vitodens; F.176 is the same finding on the 100-W and 111-W. Burner locked out. The condensate trap and drain need clearing by an engineer.Get it checked
- F.63The flue gas temperature limiter has tripped on a 2020-on Vitodens and the burner is locked out. Reset only once the flue has cooled; the cause is a circulation check for a Gas Safe engineer.Stop — call an engineer
- F.89The internal circulation pump of a 2020-on Vitodens is blocked (F.89), reporting an electrical fault (F.799) or running dry (F.982). No heating or hot water until it is freed or replaced by an engineer.Get it checked
- F0Internal fault in the burner control unit. Viessmann's only measure on the two-character units is "Replace control unit"; the Vitotronic B2HB allows one reset first. Not a householder repair.Get it checked
- E6System water pressure too low — a code only on the WB1A, early WB1B and Vitotronic 200-W. Viessmann's measure is to top up with water; later 100-W units show the flashing pressure instead.Get it checked
- F.345Temperature limiter responded on a 2020-on Vitodens, but this row releases itself after cooling. Heat is not getting away from the boiler: check pressure and bleed radiators, and call an engineer if it keeps happening.Get it checked
- F.346The combustion controller on a 2020-on Vitodens could not calibrate its ionisation current. F.372, F.464, F.468 and F.377 lock out; F.374 to F.376 restart by themselves. Gas supply, electrode, flue and condensate: engineer's checks.Stop — call an engineer
- F.369The flame lit and was lost within the safety time on a 2020-on Vitodens; F.380 is the same row. Burner locked out. Gas supply, flue recirculation and the ionisation electrode need a Gas Safe engineer.Stop — call an engineer
- F.59Mains undervoltage on a 2020-on Vitodens: the burner locks out and the pump stops until the supply recovers. If the voltage is good and it recurs, Viessmann replace the fan unit.Get it checked
- F.64Flame loss on a 2020-on Vitodens that the boiler recovered from by itself — a message, not a lockout. Worth a service visit before it becomes F.381; not a reason to reset anything.Get it checked
- F.67Ionisation current outside its permitted range on a 2020-on Vitodens; F.69, F.350 and F.351 are the same finding. The burner locks out until the electrode, gas supply and fan unit are checked by an engineer.Get it checked
- F.70An internal fault in the HBMU heat management unit of a 2020-on Vitodens. Nearly twenty numbers say the same: reset once, and if it returns the unit is replaced. Engineer only.Get it checked
- F.980Hot water stopped on a 2020-on Vitodens because the boiler could not get enough flow through itself before (F.980) or during (F.981) cylinder heating. Heating carries on. Cylinder valves, air and pump for the engineer.Get it checked
- F8The gas train closed later than the control unit expected when the burner shut down. Viessmann treat it as a gas valve fault: lockout, no reset by the householder, Gas Safe engineer.Stop — call an engineer
- FdBurner control unit fault, which Viessmann first blame on the ignition electrodes, their cables or electrical interference, and only then on the unit. FF is the same row. Engineer job.Get it checked
- 50Cylinder temperature sensor fault — 50 short circuit, 58 lead break. Heating continues; hot water from the cylinder stops until the sensor or its lead is replaced. Not a safety fault.Usually simple to fix
- F.347Flue gas recirculation detected on a 2020-on Vitodens — exhaust is getting back into the combustion air. F.463 adds contaminated air. Burner locked out; flue inspection by a Gas Safe engineer.Stop — call an engineer
- F.95The OpenTherm room controller a 2020-on Vitodens expects is not connected (F.95) or connected but not configured (F.738). On a 100-W or 111-W the burner will not run; the 050-W carries on.Get it checked
- FAThe fan did not come to rest when the control unit expected it to — "fan idle state not reached". A lockout on the fan or its control, for an engineer.Get it checked
- FCOn a 100-W, 111-W or 050-W the electrical fan control in the control unit is faulty. On a Vitotronic 200-W the same letters mean a gas train or blocked flue fault. Engineer either way.Get it checked
- b0Flue gas temperature sensor fault — b0 short circuit, b8 lead break. The burner is blocked until the sensor reads plausibly, because it is part of the flue overheat protection. Engineer job.Get it checked
- 10Outside temperature sensor fault — 10 short circuit, 18 lead break. The boiler keeps heating, in constant-temperature mode rather than weather-compensated. Not urgent; an engineer replaces the sensor.Usually simple to fix
- 51DHW outlet temperature sensor fault on a combi: 51 short circuit, 59 lead break. Heating continues but hot water stops, because the boiler cannot see the tap temperature it is controlling.Usually simple to fix
- 52Flow sensor fault on a 100-W combi: 52 is a short circuit, 5A a lead break. The burner is blocked, because the boiler cannot tell whether a tap is running. Engineer job.Get it checked
- F.102The WiFi communication module of a 2020-on Vitodens has lost contact: F.102 on the fault list, E10 or E12 during connection. Heating is unaffected; only the ViCare app link is down.Usually simple to fix
- F.370The gas or modulation valve on a 2020-on Vitodens did not close when told to; burner locked out. F.365 to F.367 are the control side. Leave the boiler off; call a Gas Safe engineer.Stop — call an engineer
- F.471The system pressure sensor is missing, open-circuit or shorted on a 2020-on Vitodens, so the boiler will not run at all. A sensor and lead check for the engineer.Get it checked
- F.68A flame signal was present before the burner started on a 2020-on Vitodens, which should be impossible, so it locked out. F.355 is the electronic version. Engineer only.Stop — call an engineer
- F5On the first-generation Vitodens 100 WB1A only, F5 is a faulty air pressure switch. No later Viessmann control unit has an F5 row; if yours shows one, check the type plate.Get it checked
- FFOn the two-character units FF is the same burner control unit fault as Fd. On a Vitotronic 200-W it means an internal fault or a disabled reset key, and Viessmann say restart the appliance.Get it checked
- 0AOn the B1HC-generation 100-W and 111-W, 0A means a fitted CO limiter has responded to carbon monoxide, or a fitted gas pressure switch has seen gas pressure fall. Switch off; Gas Safe engineer.Stop — call an engineer
- 0CMains voltage too low. The burner is blocked while the supply is out of range and restarts on its own when it recovers. Viessmann's measure on the WB1A is to contact the electricity supplier.Get it checked
- A3Flue gas temperature sensor incorrectly positioned — the sensor test at burner start saw no flame heat. Burner blocked. Viessmann: refit the sensor correctly and repeat the test.Get it checked
- F.299Real-time clock fault on a 2020-on Vitodens: the date and time are wrong. Set them again from the menu; if the boiler keeps losing time, the heat management unit's clock has failed.Usually simple to fix
- F.387Earth fault in the ionisation (flame-monitoring) circuit on a 2020-on Vitodens; F.385, F.395, F.399, F.401, F.403 and F.405 are the same family. Electrode first, heat management unit if it persists. Engineer job.Get it checked
- b7On the B1HC-generation 100-W and 111-W, b7 is emergency mode after a control unit fault and Viessmann say to switch the boiler off and on. On a Vitotronic unit it is a coding card fault.Get it checked