Viessmann Vitocal F.867 fault code

What it means

Float air-vent valve responded — air in circuit / faulty air-vent / refrigerant in float valve

The float air-vent valve in the outdoor unit has responded. On an R290 unit this can mean refrigerant has reached the float valve — treat as a possible refrigerant escape.

Safety: R290 is flammable. Escaping refrigerant can lead to explosion and serious injury — keep ignition sources away, ventilate, and follow Viessmann's refrigerant-escape procedure.

UK models this code applies to

From the Viessmann service literature we hold (Viessmann One Base service instructions 6194799 (2022), fault & warning tables (Vitocal 150-A/151-A)) — not a scraped list.

Now the harder half: proving what caused it

F.867 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.