Vaillant · Heat pumps · Vaillant aroTHERM plus with uniTOWER plus
F.741Building circuit: Return temp. too low
Name in the manufacturer's documentation (service manual): Building circuit: Return temp. too low
[1]
In plain words (editorial)
The return temperature in the heating circuit fell below 13 °C during de-icing (defrost). The compressor is blocked while the message is shown, and the message stays until the return temperature rises above 20 °C. The manual's fix includes activating the electric back-up heater to raise the return temperature, and ensuring the minimum installation volume.
When to call a service technician: If it happens repeatedly, contact a heating engineer – the system volume may be too small.
✎ editorial – written from the cited sources, not a manufacturer statement. Status: draft.
For technicians
Possible causes (source text)
- During the de-icing, the return temperature falls below 13 °C[2]
Steps given by the manufacturer (source text)
- Ensure the minimum installation volume is maintained; if required, install a series return cylinder[3]
- Activate the electric back-up heater in the product's control panel and in the system control in order to increase the return temperature. The compressor is blocked while the fault message is present.[4]
Notes from the documentation
- The fault message is displayed until the return temperature increases to above 20 °C.[5]
⚠ 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. 62 official manufacturer document quote verified
F.741 Building circuit: Return temp. too low
- [2] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified
During the de-icing, the return tem- perature falls below 13 °C
- [3] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified
Ensure the minimum installation volume is maintained; if required, install a series return cylinder
- [4] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified
Activate the electric back-up heater in the product's control panel and in the system control in order to increase the return temperature. The compressor is blocked while the fault message is present
- [5] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified
The fault message is displayed until the return temperature increases to above 20 °C