HVACopediaViessmann · Boiler
F.373 Heat transfer too low during calibration
What the control is telling you
Burner in a fault state; temperature limiter shut down.
Applies to: Vitodens 200-W B2HE 85, 120, 150, 199
Likely causes
- Poor heat transfer
- Pump scale/blockage
- 3-way valve
- Flow sensor
Test and repair steps
- Ensure adequate heat transfer.
- Check circulation pump for faults, scale or blockages.
- Test 3-way valve in actuator test and vent system.
- Check flow sensor function.
- Reset the appliance.
Models that show this code
4 models in Vitodens 200-W B2HE
Other codes on the same units
- 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
- F.377 Ionization post-adjustment conditions not met
- F.378 Flame loss during stabilization or operation
- F.379 Flame signal missing or insufficient
- F.380 Flame loss right after ignition (safety time)
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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.
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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.