HVACopediaViessmann · Boiler
F.69 Ionization current outside permitted range (valve/electrode check)
What the control is telling you
Burner in a fault state; ionization out of range.
Applies to: Vitodens 200-W B2HE 85, 120, 150, 199
Likely causes
- Insulation block touching electrode ceramic
- Gas valve leaking/faulty
- Dirty intake screen
Test and repair steps
- Check that the insulation block does not touch the electrode ceramic.
- In the actuator test run Minimum heating output for about 4 min; if the fault appears, replace the BCU.
- Switch from minimum to maximum output in the actuator test; if it faults during modulation, check the intake screen and replace the fan unit if needed.
Models that show this code
4 models in Vitodens 200-W B2HE
Other codes on the same units
- F.671 Buffer sensor TS3 short circuit
- F.672 Thermostat-function sensor TS3 open circuit
- F.673 Thermostat-function sensor TS3 short circuit
- F.68 Flame signal present at burner start
- F.691 No combustion air supply feedback
- F.7 DHW storage tank sensor open circuit
- F.70 BCU internal error
- F.71 Fan speed too low
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Viessmann Vitodens 200-W B2HE 85/120/150/199 Service Instructions 6167 813-24 (09/2026), Fault messages, p.62-73. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.