Viessmann · Heat pumps · Viessmann Vitocal 250-A (One Base, monobloc)
A.21Hydraulic system pressure too high
Name in the manufacturer's documentation (service manual): Hydraulic system pressure too high
[1]
In plain words (editorial)
The hydraulic system pressure is too high and the safety valve in the indoor unit has opened. The manual says to check the expansion vessel.
When to call a service technician: Contact your heating contractor or Viessmann technical 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] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 68 manufacturer document – copy from a distributor quote verified
A.21
- [2] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 68 manufacturer document – copy from a distributor quote verified
check the expansion vessel.
- [3] Viessmann – Service instructions: System configuration and diagnosis for heat pumps with Viessmann One Base (6194799 GB, 3/2022) (6194799 GB (3/2022)) , p. 68 manufacturer document – copy from a distributor quote verified
the safety valve in the indoor