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Vaillant · Heat pumps · Vaillant aroTHERM plus with uniTOWER plus

S.256Fan unit 1: Air inlet temp. too low

Name in the manufacturer's documentation (service manual): Fan unit 1: Air inlet temp. too low[1]

In plain words (editorial)

The compressor does not start because the air temperature at the outdoor fan is below the application limits (heating and hot water mode below -20 °C, cooling mode below 15 °C).

When to call a service technician: No action needed in extreme cold; otherwise contact a heating engineer.

✎ 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] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 57 official manufacturer document quote verified S.256 Fan unit 1: Air inlet
  2. [2] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 57 official manufacturer document quote verified The compressor does not start because the outdoor temperature
  3. [3] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 57 official manufacturer document quote verified The compressor does not start because the outdoor temperature at the fan is below the application limits