Vaillant aroTHERM F.817 fault code
Vaillant aroTHERM heat pumps
What it means
Frequency converter (inverter) fault
The frequency converter reports a compressor drive fault (F.818 mains voltage, F.819 overheating are siblings).
Safety: Safe isolation before working on the inverter — capacitors hold charge.
UK models this code applies to
From the Vaillant service literature we hold (Vaillant hydraulic station installation & maintenance instructions 0020257319 (VWL 57…127/5 IS), fault-message table) — not a scraped list.
aroTHERM plus VWL 35/6aroTHERM plus VWL 55/6aroTHERM plus VWL 75/6aroTHERM plus VWL 105/6aroTHERM plus VWL 125/6
Now the harder half: proving what caused it
F.817 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 →