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Viessmann · Boiler

F.8 DHW storage tank sensor short circuit

Medium severity Vitodens 200-W B2HE

What the control is telling you

No DHW heating; short circuit on the DHW tank temperature sensor.

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

Likely causes

  • Shorted tank sensor or wiring

Test and repair steps

  1. Check tank sensor at plug 5, wires 3 and 4.
  2. Replace the faulty part.

Models that show this code

4 models in Vitodens 200-W B2HE

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

Other codes on the same units

  • F.763 Gas pressure too high
  • F.764 Lag boiler reports a fault
  • F.765 Lead boiler communication error
  • F.77 BCU data memory error
  • F.89 Internal circulation pump blocked
  • F.91 DIO module communication error
  • F.92 ADIO module communication error
  • F.94 PlusBus voltage error

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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.