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Vaillant aroTHERM fault F.733

Evaporation temperature too low

Heat pump

What it means

Insufficient air volume flow through the outdoor unit's heat exchanger (heating mode) leads to insufficient energy input in the environment circuit (heating mode) or building circuit (cooling mode).

Likely causes

  1. Insufficient air volume flow through the outdoor unit's heat exchanger
  2. Refrigerant volume too low

Where to start

  1. If the building circuit contains thermostatic valves, check that they are suitable for cooling mode (check volume flow in cooling mode)
  2. Check the fan unit for dirt
  3. Check the EEV (does the EEV move to the limit stop? Use the sensor/actuator test)

The full answer, free

  • 5 more checks in order
  • The readings and component tests from the manual
  • The manual page for this fault (page 35), 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