Vaillant aroTHERM F.788 fault code
Vaillant aroTHERM heat pumps
What it means
Building circuit pump fault
The heating circuit pump is faulty or not responding (see also F.820 connection fault).
Safety: Isolate before working on the pump.
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 125/6aroTHERM split VWL 55/5 ASaroTHERM split VWL 105/5 ASaroTHERM split VWL 125/5 ASaroTHERM split VWL 75/5 AS
Now the harder half: proving what caused it
F.788 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.788 on your machine →Free, no sign-up. Pick the model and follow Vaillant aroTHERM's own chart for it, one question at a time.
Or watch one get chased — free demo →