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Viessmann · Heat pumps · Viessmann Vitocal 250-A (One Base, monobloc)

A.91Outside temperature too low for heat pump operation; Operation without outdoor unit, for example for screed drying; Fault refrigerant circuit

Name in the manufacturer's documentation (service manual): Outside temperature too low for heat pump operation; Operation without outdoor unit, for example for screed drying; Fault refrigerant circuit[1]

In plain words (editorial)

The outside temperature is too low for heat pump operation (this message also covers operation without the outdoor unit, e.g. for screed drying, or a refrigerant circuit fault). The refrigerant circuit switches off temporarily, and heating and hot water are provided only by the instantaneous heating water heater. The manual says no action is required.

When to call a service technician: No action needed in cold weather; if it appears in mild weather, 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. [1] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 70 manufacturer document – copy from a distributor quote verified A.91
  2. [2] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 70 manufacturer document – copy from a distributor quote verified outside temperature too
  3. [3] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 70 manufacturer document – copy from a distributor quote verified no action required
  4. [4] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 70 manufacturer document – copy from a distributor quote verified the refrigerant circuit is