Vaillant aroTHERM F.741 fault code

What it means

Building-circuit return temperature too low (during de-icing)

During de-icing the building-circuit RETURN temperature fell below 13 °C; the message stays displayed until the return rises above 20 °C, and the compressor is BLOCKED the whole time it is present. The manual's remedy: make more heat available to the de-ice — activate the electric back-up heater (product panel + system control) and check the circuit isn't starved.

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.741 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.