HVACopediaViessmann · Boiler
F.477 Solar differential temperature monitoring
What the control is telling you
Limited solar functionality.
Applies to: Vitodens 200-W B2HE 85, 120, 150, 199
Likely causes
- Solar circuit, pump or sensor fault
Test and repair steps
- Check solar circuit, solar pump and sensors.
Models that show this code
4 models in Vitodens 200-W B2HE
Other codes on the same units
- F.468 Ionization current too high during calibration
- F.471 Sensor circuit fault (call for heat)
- F.473 HMU communication error
- F.474 Program run monitoring error
- F.49 Flue gas temperature sensor open circuit
- F.5 Sensor circuit fault at plug 33 (X6)
- F.50 Flue gas temperature sensor short circuit
- F.517 Remote control not working
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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.