HVACopediaViessmann · Boiler
F.366 Gas valve supply does not switch off
What the control is telling you
Burner in a fault state.
Applies to: Vitodens 200-W B2HE 85, 120, 150, 199
Likely causes
- Faulty BCU
Test and repair steps
- Replace the BCU burner control unit (using ViGuide, per the manual's replacement note), then reset the appliance.
Models that show this code
4 models in Vitodens 200-W B2HE
Other codes on the same units
- F.355 Analogue signal reference check: flame signal at start
- F.357 Insufficient gas supply
- F.359 No ignition spark
- F.361 No or weak flame signal at burner start
- F.367 Gas valve supply does not switch off
- F.369 Flame loss right after ignition (safety time)
- F.370 Fuel or modulation valve will not close
- F.372 Repeated flame loss during calibration
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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.