Viessmann · Boiler

F.5 Sensor circuit fault at plug 33 (X6)

Low severity Vitodens 200-W B2HE

What the control is telling you

Open circuit or short on the sensor circuit wired to plug 33/X6; system keeps running on a substitute value.

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

Likely causes

Broken wire or short circuit in sensor lead

Test and repair steps

Check plug 33/X6 and its cable.
Confirm 5 V DC at plug 33 pins 1 and 2.
Switch the boiler ON/OFF switch off and on again.

Models that show this code

4 models in Vitodens 200-W B2HE

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

Other codes on the same units

F.473 HMU communication error
F.474 Program run monitoring error
F.477 Solar differential temperature monitoring
F.49 Flue gas temperature sensor open circuit
F.50 Flue gas temperature sensor short circuit
F.517 Remote control not working
F.527 Wrong HMU parameter set
F.528 Wrong BCU parameter set

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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.