Viessmann · Boiler

F.405 IO electrode ground fault

High severity Vitodens 200-W B2HE

What the control is telling you

Burner in a fault state; ground fault on ignition/ionization electrode.

Applies to: Vitodens 200-W B2HE 85, 120, 150, 199

Likely causes

Electrode ground fault
Faulty BCU

Test and repair steps

Check the electrode for a ground fault.
If it persists, replace the BCU.
Reset the appliance.

Models that show this code

4 models in Vitodens 200-W B2HE

B2HE-120B2HE-150B2HE-199B2HE-85

Other codes on the same units

F.401 IO electrode ground fault
F.402 BCU faulty
F.403 IO electrode ground fault
F.404 BCU faulty
F.406 BCU faulty
F.408 BCU faulty
F.410 BCU faulty
F.416 Flue gas temperature sensor mispositioned

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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.