Viessmann · Boiler

F.425 Time synchronization failed

Low severity Vitodens 200-W B2HE

What the control is telling you

System runs normally; calculation not working.

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

Likely causes

Time source problem

Test and repair steps

Set the time.
If an external time source is used, check parameters 1504 and 508.

Models that show this code

4 models in Vitodens 200-W B2HE

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

Other codes on the same units

F.410 BCU faulty
F.416 Flue gas temperature sensor mispositioned
F.417 BCU faulty
F.418 BCU faulty
F.430 Gateway communication error
F.446 Supply sensor / high limit deviation
F.447 Ionization current signal deviation
F.448 Ionization current signal deviation

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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.