Vaillant aroTHERM F.737 fault code

What it means

Condensation temperature too high

Condensing above the operating envelope. The manual's stated causes: the environment circuit (cooling mode) or building circuit (heating mode) is too hot for compressor operation, or external heat is being fed into the circuit.

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.

Now the harder half: proving what caused it

F.737 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.