Viessmann Vitocal F.104 fault code
Viessmann Vitocal heat pumps
What it means
External fault-message input active (EM-EA1/DIO)
Safety: Safe isolation before opening terminal covers — mains present on the interconnect.
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.104 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 →