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Vaillant · Heat pumps · Vaillant aroTHERM plus with uniTOWER plus

F.755Fault: 4-port valve position not correct

Name in the manufacturer's documentation (service manual): Fault: 4-port valve position not correct[1]

In plain words (editorial)

The 4-port (reversing) valve is not in the correct position – e.g. in heating mode the flow temperature is lower than the return temperature – or a temperature sensor shows a wrong value.

When to call a service technician: Contact a competent heating engineer (installer or Vaillant customer service).

✎ 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. 62 official manufacturer document quote verified F.755 Fault: 4-port valve position not correct
  2. [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 Incorrect position of the 4-port di- verter valve. If, in heating mode, the flow temperature is lower than the return temperature in the building cir- cuit
  3. [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 The temperature sensor in the EEV environment circuit displays an incor- rect temperature
  4. [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 Check the 4-port diverter valve (is an audible switching available? Use the sensor/actuator test)
  5. [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 Check that the coil is positioned correctly on the 4-port valve
  6. [6] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified Check the wiring harness and plug connections
  7. [7] Vaillant uniTOWER plus VIH QW 190/6 E – Operating, installation and maintenance instructions (0020291525_05) (0020291525_05) , p. 62 official manufacturer document quote verified Check the temperature sensor in the EEV environment circuit