Viessmann · Heat pumps · Viessmann Vitocal 250-A (One Base, monobloc)
F.864Outdoor unit defrost attempt unsuccessful
Name in the manufacturer's documentation (service manual): Outdoor unit defrost attempt unsuccessful
[1]
In plain words (editorial)
The outdoor unit's defrost attempt was unsuccessful. The manual says to check the outdoor unit for icing and de-ice it if necessary.
When to call a service technician: If it keeps icing up, contact your heating contractor.
✎ editorial – written from the cited sources, not a manufacturer statement. Status: draft.
The Polish page has more detail (plain-language explanation, safe checks, guides): Read in Polish →
Sources
Every statement has a footnote to the document and PDF page. “Quote verified” means the quote was found automatically in the text of that page.
- [1] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 63 manufacturer document – copy from a distributor quote verified
F.864
- [2] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 63 manufacturer document – copy from a distributor quote verified
Check outdoor unit for icing up
- [3] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 63 manufacturer document – copy from a distributor quote verified
De-ice if necessary