Viessmann Vitocal F.990 fault code
Viessmann Vitocal heat pumps
What it means
Short circuit, secondary-circuit temp sensor
The secondary-circuit temp sensor sensor reads open or short circuit.
Safety: Safe isolation before disconnecting sensors or working on the PCB.
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.
Vitocal 150-A04 (4.0 kW)Vitocal 150-A06 (4.8 kW)Vitocal 150-A08 (5.6 kW)Vitocal 150-A10 (7.3 kW)Vitocal 150-A13 (8.1 kW)Vitocal 150-A16 (9.1 kW)
Now the harder half: proving what caused it
F.990 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.
Chase this code in the app →