Vaillant · Heat pumps · Vaillant aroTHERM plus with uniTOWER plus
S.312Building circuit: Return temperature too low
Name in the manufacturer's documentation (service manual): Building circuit: Return temperature too low
[1]
In plain words (editorial)
The return temperature in the heating circuit is too low for the compressor to start (heating: below 5 °C, cooling: below 10 °C).
When to call a service technician: If it repeats, contact a heating engineer.
✎ editorial – written from the cited sources, not a manufacturer statement. Status: draft.
For technicians
Steps given by the manufacturer (source text)
- Check that the 4-port diverter valve works correctly[2]
Notes from the documentation
⚠ Work on refrigerant circuits, mains electricity and PV DC wiring is for qualified technicians only.
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] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 58 official manufacturer document quote verified
S.312 Building circuit: Return
- [2] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 58 official manufacturer document quote verified
Check that the 4-port diverter valve works cor- rectly
- [3] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 58 official manufacturer document quote verified
Return temperature in the building circuit too low for
- [4] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 58 official manufacturer document quote verified
Return temperature in the building circuit too low for compressor to start