Viessmann Vitocal F.623 fault code
Viessmann Vitocal heat pumps
What it means
Lead break, return temp (mixer HC1)
The return temp (mixer hc1) 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)Vitocal 200-S split AWB 201.D04Vitocal 200-S split AWB 201.D06Vitocal 200-S split AWB 201.D08Vitocal 200-S split AWB 201.D10Vitocal 200-S split AWB 201.D13Vitocal 200-S split AWB 201.D16
Now the harder half: proving what caused it
F.623 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 F.623 on your machine →Free, no sign-up. Pick the model and follow Viessmann Vitocal's own chart for it, one question at a time.
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