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Vaillant aroTHERM fault F.741

Building circuit: return temp. too low

Heat pump

What it means

During de-icing, the return temperature falls below 13 °C. The compressor is blocked while the fault message is present.

Likely causes

  1. During the de-icing, the return temperature falls below 13 °C
  2. Heating water leak
  3. Loss of system pressure
  4. Low or high system filling pressure
  5. Leak in heating circuit
  6. Air in system
  7. Filling pressure outside permitted range causes flashing indication
  8. Loss of heating water

Where to start

  1. Ensure the minimum installation volume is maintained
  2. Activate the electric back-up heater in the product's control panel and in the system control
  3. Check building circuit pressure via Menu → Live Monitor → Building circuit pressure

The full answer, free

  • 6 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 36), right under the answer
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Safety: Isolate the outdoor unit and any backup heater, and give the inverter capacitors time to discharge before you open the electrics. Anything on the refrigerant circuit needs F-gas certification.

From the Vaillant manual for the aroTHERM. Check the model on the data plate before you order parts.

Other Vaillant aroTHERM fault codes